Ethane dehydrogenation over CaCO₃-mediated tandem catalysts

Abstract

CO₂-assisted oxidative dehydrogenation of light alkane is a promising and innovative technology for light olefin production; however, the interference of side reactions and sluggish reactivity of CO₂ limit olefin yields. This paper describes an economically viable tandem catalytic system by coupling alkane dehydrogenation and the reverse water gas shift (RWGS) reaction, employing PtSn/SiO₂ as ethane dehydrogenation (EDH) sites and nano-CaCO₃ as the hydrogen acceptor for sequent RWGS. This tandem catalytic system significantly surpasses commercial CrO_x- and Pt-based catalytic systems, and breaks the EDH thermodynamic equilibrium limitation, reaching 142% of the nominal equilibrium ethylene yield of non-oxidative EDH process with 96.7% selectivity under industrially relevant conditions. Experimental characterization and theoretical analysis confirm that CaCO₃ mediates the pathway of hydrogen spillover that originates from adjacent PtSn/SiO₂, which effectively facilitates the RWGS reaction and thus shifts the EDH toward ethylene. This tandem catalytic strategy assisted by carbonates potentially expands the palette of catalytic systems pertaining to hydrogen transfer mechanisms in CO₂-involved hydrogenation or dehydrogenation reactions.

Introduction

Ethylene is a crucial foundational feedstock in the chemical industry^1,2. Traditional ethylene production processes, including naphtha steam cracking, Fischer-Tropsch synthesis of olefins and methanol to olefins, are afflicted by high energy consumption, numerous operating units, and low atom utilization^3,4,5,6. Ethane dehydrogenation (EDH) presents significant cost advantages in the direct conversion of ethane from shale gas into ethylene^6,7. However, the single-pass yield of ethylene in the EDH process is limited by thermodynamic equilibrium (Supplementary Fig. 1)^8,9,10,11. Taking into consideration of Le Chatelier’s principle, prompt removal of H₂ from the product mixture can shift the reaction equilibrium to enhance ethylene yield^12,13,14. Addition of the oxidant, such as O₂ is a universal method for removing H₂^15,16,17. Nevertheless, O₂ co-feeding inevitably leads to excessive oxidation of products and the risk of explosion⁵.

CO₂, which is considered a mild oxidant, is capable of avoiding the over-oxidation of products and it also holds great significance in consuming H₂ through the reverse water gas shift (RWGS) reaction^{18,19,20,21,22,23}. CO₂-assisted oxidative dehydrogenation of ethane (CO₂-ODHE) provides a higher theoretical yield of ethylene than EDH (Fig. 1a and Supplementary Figs. 2–4)^14,24. Nevertheless, the dry reforming of ethane (DRE) is thermodynamically more favorable than CO₂-ODHE (Supplementary Fig. 2: ΔG_DRE < ΔG_CO2-ODHE), which results in low ethylene selectivity and yield from ODHE due to the thermodynamic competition from DRE (Supplementary Fig. 3)^{25,26,27,28,29}. Chen et al. recently demonstrated that a PtSn/SiO₂ catalyst exhibits excellent propylene selectivity in CO₂-assisted oxidative dehydrogenation of propane (CO₂-ODHP)³⁰. However, the rate-determining RWGS reaction still limited the single-pass yield of propylene³⁰, in which the inert CO₂ molecules displayed finite removal of the H₂ generated from alkane dehydrogenation. Consequently, effective activation of CO₂ molecules is crucial for tuning hydrogen consumption and mediating the tandem process of EDH and RWGS reactions.

Fig. 1: Catalytic performance of different catalytic systems.

a Thermodynamic equilibrium compositions of CO₂-ODHE (DRE not allowed) at different temperature. The gray dashed line represented the thermodynamic equilibrium composition of ethylene in EDH. b, c Catalytic performance of PtSn/SiO₂ + CaCO₃ and commercialized catalytic systems. Conversion and selectivity (b), yield and carbon balance (c). Reaction conditions: 600 °C, a weight hourly space velocity (WHSV) of C₂H₆ equal to 8.14 h⁻¹. EDH: C₂H₆: Ar = 1:1, CO₂-ODHE: C₂H₆: CO₂ = 1:1. d Ratio of ethylene yield to traditional EDH process thermodynamic equilibrium ethylene yield for different catalytic systems. e Comparison of tandem catalyst with previously reported EDH and CO₂-ODHE catalysts, shown as pentagrams, hollow triangles, and circles, respectively. Numbers correspond to the entries in Supplementary Table 2. f Ethylene yield at different temperatures. g Long-term cyclic stability evaluation of PtSn/SiO₂ + CaCO₃, PtSn/SiO₂, and PtSn/γ-Al₂O₃ systems. Reaction conditions: T = 600 °C, catalyst: 200 mg, total flow rate of 20 mL/min, Ar balanced (50% C₂H₆, 50% CO₂; 50% C₂H₆, 10% CO₂; 50% C₂H₆, 25% CO₂; 75% C₂H₆, 25% CO₂).

CaCO₃ is a low-cost and common material in integrated CO₂ capture and utilization, which can act as a reversible carrier for gas-solid carbonate hydrogenation in the calcium looping process^{31,32,33,34,35}. Thermodynamically, the decomposition of CaCO₃ is apparently expedited in the presence of H₂ (Supplementary Fig. 5), inferring that CaCO₃ might be a potential hydrogen acceptor. Moreover, solid carbonates can heuristically serve as intermediate regulators that are favorable to CO₂-involved reactions. For instance, Xia et al. observed that the chemical activation of CO₂ molecules in the form of carbonates on PbO facilitated the CO₂ reduction reaction toward HCOOH³⁶. Here, we describe a tandem process of alkane dehydrogenation and the RWGS reaction over CaCO₃ coupled with PtSn/SiO₂ catalysts to enhance ethylene yield (Supplementary Fig. 6). In the tandem catalytic system, PtSn/SiO₂ converts ethane into ethylene and hydrogen species (H*), while the adjacent CaCO₃ induces H* to migrate from the dehydrogenation sites to react with solid carbonates, generating H₂O and CO via the RWGS reaction. Simultaneously, the CO₂ molecules are trapped by vacancies in CaCO₃ to complete the redox cycle. Under near-realistic and challenging conditions of high space velocity and high ethane concentration, the tandem catalyst achieves 31.9% ethylene single-pass yield with 96.7% ethylene selectivity, exceeding the equilibrium yield of the non-oxidative EDH process and closely approaching the equilibrium of CO₂-ODHE. The ethylene space-time yield (STY) is respectively 112- and 1.6-fold higher than that of commercial CrO_x- and Pt-based catalysts under equivalent conditions. In addition, energy consumption and net CO₂ emissions of the tandem catalytic system were also significantly lower than those of commercial PtSn/γ-Al₂O₃ catalytic EDH system.

Results

Catalytic performance in CO₂-ODHE

The catalytic performances of different catalytic systems were tested on stream of 50 vol.% C₂H₆ balanced with either Ar or CO₂ at 600 °C. In the absence of CO₂, PtSn/SiO₂ attained high ethylene selectivity (98.5%) at 22.4% ethane conversion that approached thermodynamic equilibrium of EDH (22.5%), comparable to commercial PtSn/γ-Al₂O₃ (Fig. 1b and Supplementary Fig. 7). After co-feeding CO₂ with ethane, PtSn/SiO₂ presented 26.2% ethylene yield with 96.0% ethylene selectivity, breaking the thermodynamic equilibrium limit of EDH (Fig. 1c). When coupling PtSn/SiO₂ with CaCO₃, we noted that the H₂ yield decreased at the increased conversions of ethane and CO₂, and the highest ethylene yield (selectivity) of 31.9% (96.7%) was obtained (Fig. 1b, c). This reached 142% of the nominal equilibrium ethylene yield of EDH (Fig. 1d), outperforming the commercial CrO_x- and Pt-based catalytic systems, as well as other previous reported catalysts (Fig. 1e and Supplementary Table 2). Moreover, the ethylene yields of PtSn/SiO₂ + CaCO₃ tandem catalyst were near the thermodynamic equilibrium values of CO₂-ODHE across different temperatures (450–650 °C) and ethane volume fractions (10–50%) (Fig. 1f and Supplementary Fig. 8). The carbon balance in C_xH_y and total carbon balance of PtSn/SiO₂ + CaCO₃ tandem catalyst reached 99.1% and 99.0%, respectively (Supplementary Fig. 9), demonstrating the negligible influences of DRE and deep dehydrogenation side reactions during CO₂-ODHE. We found an induction period of C₂H₆ and CO₂ conversions over PtSn/SiO₂ + CaCO₃ tandem catalysts in the initial 30 min of reaction, and in situ X-ray diffraction (in situ XRD) confirmed that this stage corresponds to the transformation of CO₂ into carbonate (Supplementary Fig. 10). CaCO₃ alone produced 0.9% ethylene yield at 600 °C (Fig. 1f), implying CaCO₃ is inclined to function as a hydrogen acceptor rather than an EDH site.

Concerning the evaluation of ethylene productivity, ethylene STY was calculated to reach 7.81 mol C₂H₄ g_metal⁻¹ h⁻¹ (78.1 mmol C₂H₄·g_cat⁻¹·h⁻¹) upon tandem catalyst, which was 112 and 1.6 times higher than those of the commercial CrO_x- and Pt-based catalytic systems, respectively (Fig. 1d). The STY was significantly higher than those reported catalysts for CO₂-ODHE, EDH, and O₂-ODH (Supplementary Table 2). In addition, for CO₂-ODHP, the tandem catalyst exhibited exceptional catalytic activity with 94.5% propylene selectivity and 55.0% single-pass propylene yield (Supplementary Fig. 11), which moved beyond the thermodynamic equilibrium of direct propane dehydrogenation (PDH, 48.0%) at 550 °C (Supplementary Fig. 4), surpassing the values reported in the previous literature (Supplementary Fig. 12 and Supplementary Table 3).

For the long-term cyclic stability at 600 °C, the tandem catalyst showed a slightly declined ethane conversion that remained higher than the equilibrium of non-oxidative EDH process (22.5%), whereas the commercial PtSn/γ-Al₂O₃ and K-CrO_x/γ-Al₂O₃ showed rapid deactivation during 10 h at high ethane concentration and weight hourly space velocity (50 vol.% C₂H₆, WHSV = 8.14 h⁻¹) (Fig. 1g and Supplementary Fig. 13). Notably, the deactivation constant (k_d) of PtSn/SiO₂ + CaCO₃ was only 0.046 h⁻¹, much lower than that of the commercial PtSn/γ-Al₂O₃ (0.121 h⁻¹) and K- CrO_x/γ-Al₂O₃ (0.331 h⁻¹) under the same conditions (Supplementary Fig. 14). In addition, the PtSn/SiO₂ + CaCO₃ tandem catalytic system offers significant advantages in terms of energy consumption and net CO₂ emissions compared to the commercial PtSn/γ-Al₂O₃ catalytic system, with energy savings of about 8.3% and CO₂ emission reductions of 60.6% for ethylene production per unit (Supplementary Fig. 15). This suggests that the catalytic performance and economic potential of our proposed tandem catalytic process has a significant advantage over commercial catalytic systems under near-realistic and challenging operating conditions. We also evaluated the cyclic stability of the tandem catalyst for CO₂-ODHE under various feed conditions (high ethane/CO₂ ratios, 75% high concentration of ethane). After several regeneration cycles, the catalytic performance was basically restored (Fig. 1g). To verify the potential of the tandem catalytic system for industrial scale-up, we appropriately increased the reactor scale (total flow rate: 400 mL/min) and tested its catalytic performance (Supplementary Fig. 16). The ethane conversion, ethylene selectivity, and stability were almost identical to the results obtained in the laboratory-scale reactor.

Structural characterization of tandem catalysts

XRD and high-resolution transmission electron microscope (HRTEM) of PtSn/SiO₂ showed that the PtSn nanoparticles were uniformly dispersed on the amorphous SiO₂ support (Supplementary Figs. 17 and 18). For the tandem catalyst, high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) and energy-dispersive X-ray spectroscopy (EDX) images discerned independent nano-CaCO₃ (ca. 52 nm) and highly dispersed PtSn nanoparticles (ca. 1.9 nm) on SiO₂ with nanoscale intimacy (Fig. 2b–g and Supplementary Figs. 19–23), as described in Fig. 2a. The shortest distance between PtSn nanoparticles and CaCO₃ was less than 1 nm in the analysis of the HRTEM image (Fig. 2h and Supplementary Fig. 23). Pt 4f X-ray photoelectron spectroscopy (XPS) and Pt L₃-edge X-ray absorption near-edge structure (XANES) spectra verified the electron transfer from Sn to Pt in the PtSn/SiO₂ and tandem catalyst, possibly due to the alloying effect of PtSn (Fig. 2i and Supplementary Fig. 24)^37,38, as evidenced by the Pt-Sn bond formation determined by Pt L₃-edge extended X-ray absorption fine structure (EXAFS) spectra and wavelet transform (Fig. 2j and Supplementary Fig. 25)^37,39. Importantly, the chemical states of Pt and Sn would not be subject to physical integration with CaCO₃, as sustained by XPS and Pt L₃-edge XANES spectra (Supplementary Figs. 24–27 and Supplementary Table 6). In addition, a J factor was defined as the ratio of CN_Pt-Sn/ (CN_Pt-Sn + CN_Pt-Pt) versus the theoretical value of thermally stable phase (Supplementary Table 7)^30,40. As J_Pt3Sn was close to 1, Pt₃Sn was affirmed as the main phase in PtSn/SiO₂ and the tandem catalyst, consistent with the results of HRTEM. We also conducted in situ ambient pressure XPS to further investigate the valence states of Pt and Sn during the CO₂-ODHE (Supplementary Fig. 28). The difference in the binding energy shifts of Pt 4f in Pt/SiO₂ and PtSn/SiO₂ after introducing the reaction gas indicates that the PtSn alloy effect weakens the interaction between Pt and H*²⁰.

Fig. 2: Structural Characterizations of PtSn/SiO₂ + CaCO₃ tandem catalyst.

a Schematic spatial distribution of PtSn/SiO₂ + CaCO₃. b–h HAADF-STEM images (b, c), EDX-mappings (d–g) and HRTEM image (h) of PtSn/SiO₂ + CaCO₃. The inset in (c) shows the size distribution of Pt₃Sn nanoparticles. The inset in (h) shows Inverse Fast Fourier Transform (IFFT) processing of single Pt₃Sn nanoparticle from the selected square area. i, j Normalized Pt L₃-edge XANES spectra (i) and k²-weighted Pt L₃-edge EXAFS spectra (j) of PtSn/SiO₂, PtSn/SiO₂ + CaCO₃ and reference samples.

To investigate the cause of catalyst deactivation, we conducted HRTEM, HAADF-STEM, EDS mapping, solid-state NMR, and Raman spectroscopy on both the spent and regenerated catalysts. The XRD, HAADF-STEM, HRTEM, and EDS mapping results indicated that the structure of the catalyst and the size of PtSn particles remained unchanged after 10 h of reaction and subsequent regeneration (Supplementary Figs. 29–32). However, Raman spectroscopy revealed the presence of defective carbon (D band: 1326 cm⁻¹) and graphitic carbon (G band: 1594 cm⁻¹) on spent catalysts (Fig. 3a)²⁹. Notably, individual PtSn/SiO₂ and the tandem catalyst showed similar defective and graphitic carbon contents and I_D/I_G, indicating that the introduction of CaCO₃ does not affect the coke-induced deactivation of PtSn/SiO₂. Compared to the commercial PtSn/γ-Al₂O₃ system, the tandem catalytic system exhibited lower coke content, which accounts for the lower k_d observed. Solid-state NMR analysis showed abundant saturated aliphatic carbon species on the spent tandem catalyst (Supplementary Fig. 31), suggesting that coke formation may be associated with ethylene polymerization products at high temperature⁴¹. Additionally, O₂-TPO analysis of spent catalysts after different reaction times revealed that coke accumulation increased with reaction time, although the deposition rate gradually slowed (Supplementary Fig. 33). The accumulation of the coke may cover the active sites and lead to catalyst deactivation^19,42. However, after the regeneration, the disappearance of graphite carbon and defective carbon on the catalyst indicated that the coke was completely removed, thereby restoring the catalytic activity.

Fig. 3: Catalyst deactivation and kinetic studies.

a Raman spectra of PtSn/γ-Al₂O₃, PtSn/SiO₂, PtSn/SiO₂ + CaCO₃ catalysts after 10 h of reaction and PtSn/SiO₂ + CaCO₃ after regeneration. b, c Catalytic performance of tandem catalysts comprising PtSn/SiO₂ and CaCO₃ with different integration manners in EDH or CO₂-ODHE. b Ethane conversion, CO₂ conversion, and ethylene selectivity. c Ethylene yield, H₂ yield, and carbon balance in C_xH_y. Reaction conditions: T = 600 °C, WHSV = 8.14 h⁻¹, total gas flow rate of 20 mL/min. d, e Effect of the ethane (d) and CO₂ (e) partial pressure on the ethane conversion over different catalysts. Reaction conditions: T = 600 °C. f Arrhenius plots of different catalytic systems.

Importance of CaCO₃ integrated with PtSn/SiO₂

Temperature-programmed surface reaction (TPSR) of C₂H₆/CO₂ (Ar) showed that the introduction of CaCO₃ significantly increased the yield of ethylene by PtSn/SiO₂, accompanied by noticeable consumption of CO₂ and decreased production of H₂. This suggests that CaCO₃ refines the process of RWGS in CO₂-ODHE (Supplementary Fig. 34). For the tandem catalyst, H₂ and CO₂ conversion of 36.0% and 35.4%, respectively, approached the thermodynamic equilibrium value of RWGS (38.3%) at 600 °C (Supplementary Fig. 35), higher than those of PtSn/SiO₂ without CaCO₃ (28.7% H₂ and 28.2% CO₂ conversion). These results are mutually corroborated with the improved performance in the CO₂-ODHE mediated by the integration of CaCO₃.

For manipulating the distance between dehydrogenation sites and the CaCO₃ hydrogen acceptor, we coupled PtSn/SiO₂ with CaCO₃ in three tandem modes denoted as M₁, M₂, and M₃ (Fig. 3b, c)¹³. Based on Monte Carlo estimations, the distances between the two components in M₁, M₂, and M₃ are approximately 2.4 mm, 472.8, and 43.6 μm, respectively (Supplementary Fig. 36). A strong correlation was found between the distance of PtSn/SiO₂ and CaCO₃ and the catalytic performance. As the distance between PtSn/SiO₂ and CaCO₃ decreases, the ethane reaction rate, ethylene selectivity, and CO₂ conversion significantly increase (M₃ > M₂ > M₁), accompanied by lower H₂ yield (Supplementary Fig. 37). According to the concept of “the closer, the better” for tandem sites⁴³, the shorter distance between reactive centers is conducive to the migration of intermediates or active species. Therefore, we ascribe this proximity-dependent phenomenon to the intensified intermediate species spillover between PtSn/SiO₂ and CaCO₃ at the nanoscale.

We conducted kinetic experiments to further investigate the crucial role of CaCO₃ in the CO₂-ODHE. At 600 °C, by varying the partial pressure of C₂H₆ or CO₂, we determined the reaction orders of ethane and CO₂ over PtSn/SiO₂ and the tandem catalyst, as shown in Fig. 3d, e. The reaction orders of ethane were significantly higher than those of CO₂ (0.84  > 0.16, 0.75  > 0.33). The ethane reaction rate increased with increasing CO₂ partial pressure, which can be attributed to the consumption of H* by CO₂ via the RWGS reaction, thereby promoting ethane conversion Notably, the reaction order of CO₂ on the tandem catalyst (n_CO2 = 0.16) was lower than that on PtSn/SiO₂ (n_CO2 = 0.33), suggesting that the incorporation of CaCO₃ reduces the dependence of ethane conversion on CO₂ partial pressure. In addition, we tested the apparent activation energies (E_a) of ethane over the tandem catalyst and PtSn/SiO₂ (in the presence and absence of CO₂) (Fig. 3f). For PtSn/SiO₂, the introduction of CO₂ significantly lowered the E_a from 127.2 kJ/mol (without CO₂) to 111.2 kJ/mol (with CO₂). After the tandem integration of CaCO₃ and PtSn/SiO₂, the E_a was further reduced to 84.8 kJ/mol, indicating that CaCO₃ can activate CO₂ to further consume H^* and thereby improve ethylene production. The kinetic analysis of propane revealed similar trends (Supplementary Fig. 38), confirming the mechanistic consistency of the tandem catalyst in promoting alkane conversion.

Mechanistic studies of hydrogen spillover-mediated EDH and RWGS

The smooth migration of intermediates or H* species between reactive sites in closer proximity over the nanoscale tandem catalyst is of paramount importance to accelerate tandem catalytic coupling processes^13,44,45. For EDH, the kinetic analysis indicated that promptly removing H₂ or H* from the dehydrogenation sites can enhance the reaction rate of EDH to ethylene (Supplementary kinetic analysis). We performed H₂-TPR and NH₃ temperature-programmed reduction (NH₃-TPR) to validate the spillover performance of hydrogen intermediates on the tandem catalyst (Fig. 4a and Supplementary Fig. 39). The temperature of reduction peak over CaCO₃ decreased from 726 °C to 671 °C when coupling with PtSn/SiO₂ (Fig. 4a). As shown by mass spectrometry, hydrogenation products formed more easily at a lower temperature on the tandem catalyst compared with individual CaCO₃.

Fig. 4: Carbonates-induced hydrogen spillover between PtSn/SiO₂ and CaCO₃.

a H₂-TPR profiles of PtSn/SiO₂ + CaCO₃ and CaCO₃. b, c In situ XRD patterns of PtSn/SiO₂ + CaCO₃ (b) and CaCO₃ (c) under 10 vol.% H₂/Ar at 600 °C. d XRD patterns of PtSn/SiO₂ + CaCO₃ after different reaction states. e ¹³CO₂/H₂-TPSR of PtSn/SiO₂ + CaCO₃. f Schematic of tandem coupling of EDH and RWGS over PtSn/SiO₂ + CaCO₃. g–i In situ DRIFTs of PtSn/SiO₂ + CaCO₃ (g), PtSn/SiO₂ (h), and relative content of Si-OH (i) under 10 vol.% C₂H₆ at 600 °C. The inset schematic in (i) depicts the evolution processes of Si-OH over PtSn/SiO₂ + CaCO₃.

H₂-TPR for tandem catalyst with different tandem modes also reflects that the distance between two components is strongly interrelated to hydrogen spillover (Supplementary Fig. 40). Specifically, as the distance between the components decreases, the reduction temperature of CaCO₃ shifts earlier, which is attributed to the enhanced hydrogen spillover from PtSn/SiO₂ to CaCO₃. For tandem catalyst, the H₂ signal increased slowly initially, while CO and H₂O signals exhibited a rapid rise, suggesting a higher rate of CaCO₃ hydrogenation in the presence of PtSn/SiO₂ (Supplementary Fig. 41). In situ XRD under H₂/Ar at 600 °C (Fig. 4b, c) and ex situ Raman Spectroscopy (Supplementary Fig. 42) demonstrated that CaCO₃ in the tandem catalyst was completely reduced into CaO at 600 °C within approximately 60 min in contrast to the poor reducibility of individual CaCO₃. These results hint that the occurrence of hydrogen spillover induced by nanoscale contact between two components in the tandem catalyst should result in the acceleration of the CaCO₃ hydrogenation rate.

To deeply delve into the role of CaCO₃ in the hydrogen spillover process, we switched the reaction atmospheres and observed the changes of it during CO₂-ODHE (Fig. 4d). XRD revealed that CaCO₃ was first reduced to CaO via H₂/Ar pretreatment. When switching to C₂H₆/CO₂, CaO rapidly underwent carbonation back to CaCO₃, corresponding to the induction period in the former 30-min reaction of CO₂-ODHE (Supplementary Fig. 10). This suggests that the supplement of CO₂ is faster than consumption, leading to the existence of CaCO₃ under the reaction condition. Subsequently, on exposure to C₂H₆/Ar, the CaO phase reappears. Isotopic ¹³CO₂ and H₂ TPSR (¹³CO₂-H₂/TPSR) on the tandem catalyst indicated that the RWGS reaction dominated below 485 °C with ¹³CO as the main products (Fig. 4e). In the temperature range of 485–650 °C, ¹²CO signal increased continuously while ¹³CO signal remained almost unchanged, illuminating that H* preferably reacts with the carbonates in CaCO₃ rather than ¹³CO₂ molecules. Therefore, we conclude that the active carbonates in CaCO₃ are responsible for driving hydrogen spillover and rapidly consuming H* to reinforce the equilibrium shift of CO₂-ODHE. Subsequently, the reduced CaCO₃ captures CO₂ molecules to accomplish the regeneration cycle of carbonates, as illustrated in Fig. 4f.

In situ diffuse reflectance infrared Fourier transform (DRIFT) experiments further unravel the hydrogen spillover mediated by carbonates in CaCO₃ during CO₂-ODHE (Fig. 4g, h). After feeding ethane at 600 °C, the signals at 3728–3734 cm⁻¹ assigned to the Si−OH groups^46,47 were observed in both the tandem catalyst and individual PtSn/SiO₂. The relative content of Si−OH species over individual PtSn/SiO₂ rapidly increased to 87.8% of the infrared signal during the steady state within 15 min (Fig. 4i). In contrast, the Si-OH species on the tandem catalyst increased slowly and accounted for only 16.8% of the integral intensity of the steady state, pointing to the fact that the adjacent CaCO₃ with nanoscale proximity triggers H* migration from the Pt₃Sn sites toward carbonates producing CO (2110 cm⁻¹ and 2175 cm⁻¹)⁴⁸, thus expediting the removal of H*. After the 15-min period, the continuous consumption of carbonates without replenishment leads to weakened impetus for H* spillover, accounting for the rapid increase of Si-OH content.

Theoretical study

Density functional theory (DFT) calculations were carried out on the surface of CaCO₃ (010) and Pt₃Sn (100) (Supplementary Fig. 43). Figure 5a presents a uniform charge distribution in CO₂ molecule, with both C = O bond lengths of 1.18 Å. Comparably, the carbonate of CaCO₃ due to uneven charge distribution was comprised of three distinct C−O linkages with relatively elongated bond lengths of 1.27, 1.31, and 1.32 Å, enabling the easier activation of C−O bonds per se. Potential density of states (PDOS) analysis (Fig. 5b) demonstrates a more dispersive electron distribution in carbonates of CaCO₃, confirming the weaker strength of C−O bonds in carbonates compared with CO₂ molecules. Collectively, we infer that carbonates within CaCO₃ are more accessible to undergo the RWGS reaction compared with CO₂ molecules. Notably, the hydrogen adsorption on O-CaCO₃ (−1.12 eV) was considerably stronger than those on Ca-CaCO₃ (−0.26 eV), C-CaCO₃ (−0.62 eV), Pt–Pt₃Sn (−0.79 eV), and Sn–Pt₃Sn (–0.71 eV) (Fig. 5c and Supplementary Fig. 44), illustrating that the hydrogen spillover from Pt₃Sn sites to O-CaCO₃ is thermodynamically favorable.

Fig. 5: Theoretical study of DFT calculations in CO₂-ODHE.

a Microstructure and charge density difference between carbonates in CaCO₃ and CO₂ molecules. b PDOS for carbonates in CaCO₃ and CO₂ molecules. c Hydrogen adsorption energy on the O-CaCO₃, Ca-CaCO₃, C-CaCO₃, Pt-Pt₃Sn, and Sn-Pt₃Sn. d Calculated relative energy diagrams of EDH on Pt₃Sn clusters. e Calculated relative energy diagrams of the reaction between H* and CO₂ molecules on Pt₃Sn. f Calculated relative energy diagrams of the reaction between H* and carbonates in CaCO₃ and CO₂ molecules replenishment of vacancies. Insets in (d–f) are the corresponding structures along the reaction paths. IS indicates the initial state, and TS indicates the transition state. Color scheme: red, gray, white, green, purple, and blue balls stand for O, C, H, Ca, Pt, and Sn atoms, respectively.

The molecular-level details of EDH and RWGS processes were elaborated through the calculation of relative energy. For the EDH process, ethane is first adsorbed onto the Pt₃Sn site and then dehydrogenated to form ethylene and hydrogen (Fig. 5d and Supplementary Figs. 45 and 46). The highest energy barrier in this reaction corresponds to the first C-H bond cleavage of ethane (TS1 in Fig. 5d, E₀ = 1.67 eV), which aligns with the kinetic observation that the reaction order of ethane is relatively high. In addition, the energy barrier for hydrogen formation is 1.56 eV (TS3 in Fig. 5d, E₁). In the reaction pathway of RWGS involving CO₂ molecules on the Pt₃Sn surface, the formation of COOH* from H* and CO₂* is the rate-determining step (TS1 in Fig. 5e, E₂ = 1.47 eV), with a lower energy barrier than hydrogen formation in the EDH process, indicating CO₂ is kinetically viable to consume H*. In contrast, the RWGS process steered by CaCO₃ involving H* and carbonates requires a much lower energy barrier (TS2 in Fig. 5f, E₃ = 1.38 eV, E₃ < E₂ < E₁). This is consistent with the kinetic results showing that the E_a of the tandem catalyst is significantly lower than that of the individual PtSn/SiO₂ catalyst (84.8 kJ/mol <111.2 kJ/mol). Therefore, H* is energetically favored to undergo RWGS with the carbonates in CaCO₃, which is consistent with the results of ¹³CO₂-H₂/TPSR. In this process, H* adsorption steps are exothermic, suggesting the feasibility of hydrogen spillover from Pt₃Sn sites to CaCO₃. Based on the above calculation results, we propose a reaction mechanism of the CO₂-ODHE process. Pt₃Sn serves as the dehydrogenation site to convert ethane into ethylene and H*. Subsequently, H* spills over to the nanoscale-adjacent CaCO₃ and reacts with carbonates via RWGS to produce H₂O and CO. Finally, CO₂ replenishes the vacancies in CaCO₃ to complete the cycle.

Related tandem catalysts

To assess the generality of hydrogen spillover effects over carbonate-mediated tandem catalytic systems, we utilized other alkaline earth metal carbonates (such as MgCO₃, SrCO₃, and BaCO₃) to replace CaCO₃ as hydrogen acceptors in the tandem catalyst. As expected, these carbonates consumed hydrogen to varying degrees, thereby increasing the ethylene single-pass yield. All tandem catalysts showed enhanced ethylene yield that exceeded the non-oxidative EDH process equilibrium value (22.5%), with selectivity greater than 93% (Supplementary Figs. 47 and 48). These results support the universal principle of carbonate-induced hydrogen spillover in heterogeneous catalysis.

Discussion

We describe a CaCO₃-mediated strategy for tandem catalytic process of EDH and RWGS to tackle the imposing constraint on the selectivity and yield of ethylene in CO₂-ODHE. PtSn/SiO₂ coupled with nanoscale-adjacent CaCO₃ achieved 31.9% ethylene single-pass yield with 96.7% ethylene selectivity under industrially relevant conditions, exceeding the equilibrium yield of the non-oxidative EDH process and outperforming commercial CrO_x- and Pt-based catalyst systems. Moreover, the tandem catalytic system showed lower energy consumption and net CO₂ emissions compared to commercial PtSn/γ-Al₂O₃ catalytic EDH system. The comprehensive studies elucidate that PtSn/SiO₂ catalyzes EDH to produce ethylene and H*, while the intrinsic carbonates in CaCO₃ induce H* migration and thus shift the CO₂-ODHE toward high-efficiency ethylene production. Simultaneously, the carbonates in CaCO₃ could be reversibly replenished by CO₂ molecules to complete the cycle. This tandem catalytic system also works efficaciously for CO₂-ODHP to produce propylene. Our study offers an inspiration for catalyst design with application in the reactions involving hydrogen transfer catalysis and processes.

Methods

Preparation of tandem catalysts

The tandem catalysts comprising PtSn/SiO₂ and nano-CaCO₃ (average particle size of 50 nm, Macklin) were prepared by physical mixing. The actual contents of Pt and Sn in PtSn/SiO₂ were determined by inductively coupled plasma mass spectrometry to be 0.98 wt% and 0.59 wt%, respectively. The control of the spatial distribution distance between PtSn/SiO₂ and CaCO₃ were prepared by three different tandem modes. M₁: initially, PtSn/SiO₂ and nano-CaCO₃ were individually pressed, crushed, and sieved to granules between 20 and 40 mesh, respectively. Subsequently, PtSn/SiO₂ granules were placed on the top layer, CaCO₃ granules were placed on the bottom layer, and a quartz wool layer approximately 2 mm thick was used to separate the two layers. M₂: the equal mass sieved PtSn/SiO₂ (20–40 mesh) and nano-CaCO₃ (20–40 mesh) were placed into a 10 mL centrifuge tube, followed by shaking to ensure homogeneous mixing. M₃: equal masses of PtSn/SiO₂ and nano-CaCO₃ powders were ground together in the agate mortar for 10 min and then placed into a 10 mL centrifuge tube, followed by shaking to achieve uniform mixing. Subsequently, the obtained mixtures were pressed, crushed, and sieved to granules between 20 and 40 mesh. Tandem catalysts were mixed using the M₃ method unless otherwise specified.

Preparation of commercial catalyst analogues

Common commercial catalyst analogues in EDH (PDH) system are PtSn/γ-Al₂O₃ and K-CrO_X/Al₂O₃. In a typical synthesis of PtSn/γ-Al₂O₃^9,38, H₂PtCl₆ (Macklin) and SnCl₄·5H₂O (Meryer) were added to a 0.1 M HCl solution and ultrasonically mixed for 30 min in which the final molar concentration of Pt and Sn ions were 102 mM and 510 mM. Then, 1 mL of the above solution was diluted to 40 mL of deionized water, which was added to 2 g of γ-Al₂O₃ and stirred at room temperature for 12 h. The theoretical loading of Pt was controlled at 1%. For synthesis of K-CrO_x/Al₂O₃^17,47, 1.58 g of γ-Al₂O₃ support was dissolved in 40 mL of deionized water, followed by the addition of 3.08 g of Cr(NO₃)₃·9H₂O (Meryer) and 0.05 g of KNO₃ (Meryer), and stirred at room temperature for 12 h. The theoretical loadings of Cr and K were controlled at 20% and 1%, respectively. The above solution was dried overnight at 373 K. Finally, the obtained solid was calcined in air at 550 °C for 3 h.

Catalytic performance tests

The EDH and CO₂-ODHE catalytic performance were conducted in a continuous flow fixed-bed reactor at atmospheric pressure¹³. Typically, 0.1 g of PtSn/SiO₂ and 0.1 g of nano-CaCO₃ (or other mixtures) composing the tandem catalyst (20–40 mesh) were placed in a quartz tube (inner diameter 8 mm), with quartz wool filled both above and below the tandem catalyst. The temperature of the catalyst bed was controlled by a K-type thermocouple. The catalyst was pretreated in 10 vol.% H₂/Ar (30 mL/min) at 600 °C for 2 h, followed by Ar (50 mL/min) purging for 10 min. Next, the specified reaction conditions (C₂H₆: CO₂ = 1:1, total flow rate of 20 mL/min) was switched into the reactor and stabilized for 30 min. The effluent from the reactor outlet was thoroughly mixed with pure N₂ (5 mL/min) before entering the gas chromatograph (GC) for analysis. For the tests at different temperatures, the gas composition and catalyst loading were consistent with the above conditions, except that the reaction temperature was decreased to the desired value (450–650 °C) and data points were collected after stabilization for 30 min. For tests with different ethane volume fractions, the flow rates of C₂H₆ and CO₂ were adjusted to 10, 8, 6, 4, and 2 mL/min, respectively, while Ar was used as a balance gas with flow rates of 0, 4, 8, 12, and 16 mL/min, maintaining a total flow rate of 20 mL/min. For the tests on individual PtSn/SiO₂, SiO₂ was used instead of CaCO₃ to mix with PtSn/SiO₂. For EDH tests, Ar was used instead of CO₂ to mix with C₂H₆ (C₂H₆: Ar = 1:1). For RWGS tests, H₂ was used instead of C₂H₆ to mix with CO₂ (H₂: CO₂ = 1:1).

The products were analyzed by an online GC (F70, Fuli Instruments) equipped with Pora PLOT Q column (CH₄, C₂H₄, C₂H₆, C₃H₆, and C₃H₈), another Pora PLOT Q column (CO and CO₂), and MS 5 A Plot column (H₂ and N₂). N₂ was used the internal standard for GC quantification of all gases. The C₂H₆ conversion (Eq. (1)), CO₂ conversion (Eq. (2)), C₂H₄ yield (Eq. (3)), H₂ yield (Eq. (4)), C₂H₄ selectivity in C_xH_y (Eq. (5)), total C₂H₄ selectivity (Eq. (6)), carbon balance in C_xH_y (Eq. (7)), and total carbon balance (Eq. (8)) were defined as follows^13,21:

$${{{{\rm{C}}}}}_{2}{{{{\rm{H}}}}}_{6}\,{{{\rm{conversion}}}}\,(\%)=\frac{{F}_{{{\mbox{C}}}_{2}{{\mbox{H}}}_{6}}^{{\mbox{in}}}-{F}_{{{\mbox{C}}}_{2}{{\mbox{H}}}_{6}}^{{\mbox{out}}}}{{F}_{{{\mbox{C}}}_{2}{{\mbox{H}}}_{6}}^{{\mbox{in}}}}\times 100$$

(1)

$${{{{\rm{CO}}}}}_{2}\,{{{\rm{conversion}}}}\,(\%)=\frac{{F}_{{{\mbox{C}}}{{\mbox{O}}}_{2}}^{{\mbox{in}}}-{F}_{{\mbox{C}}{{\mbox{O}}}_{2}}^{{\mbox{out}}}}{{F}_{{{\mbox{C}}}{{\mbox{O}}}_{2}}^{{\mbox{in}}}}\times 100$$

(2)

$${{\mbox{C}}}_{2}{{\mbox{H}}}_{4}\,{{\mbox{yield}}}\,\left(\%\right)=\frac{{F}_{{{\mbox{C}}}_{2}{{\mbox{H}}}_{4}}^{{\mbox{out}}}}{{F}_{{{\mbox{C}}}_{2}{{\mbox{H}}}_{6}}^{{\mbox{in}}}}\times 100$$

(3)

$${{\mbox{H}}}_{2}\,{{\mbox{yield}}}\,\left(\%\right)=\frac{{F}_{{{\mbox{H}}}_{2}}^{{\mbox{out}}}}{{F}_{{{\mbox{C}}}_{2}{{\mbox{H}}}_{6}}^{{\mbox{in}}}}\times 100$$

(4)

$${{\mbox{C}}}_{2}{{\mbox{H}}}_{4}\,{{\mbox{selectivity}}}\,\left(\%\right)\,{{\mbox{in}}}\,{{\mbox{C}}}_{{\mbox{x}}}{{\mbox{H}}}_{{\mbox{y}}}=\frac{2\times {F}_{{{\mbox{C}}}_{2}{{\mbox{H}}}_{4}}^{{\mbox{out}}}}{{F}_{{\mbox{C}}{{\mbox{H}}}_{4}}^{{\mbox{out}}}+2\times {F}_{{{\mbox{C}}}_{2}{{\mbox{H}}}_{4}}^{{\mbox{out}}}}\times 100$$

(5)

$${{\mbox{Total}}}\,{{\mbox{C}}}_{2}{{\mbox{H}}}_{4}\,{{\mbox{selectivity}}}\,\left(\%\right)=\frac{{{\mbox{C}}}_{2}{{\mbox{H}}}_{4}\,{{\mbox{yield}}}\,\left(\%\right)}{{{\mbox{C}}}_{2}{{\mbox{H}}}_{6}\,{{\mbox{conversion}}}\left(\%\right)}\times 100$$

(6)

$${{\mbox{Carbon}}}\,{{\mbox{balance}}}\,\left(\%\right)\,{{\mbox{in}}}\,{{\mbox{C}}}_{{\mbox{x}}}{{\mbox{H}}}_{{\mbox{y}}}=\frac{{F}_{{\mbox{C}}{{\mbox{H}}}_{4}}^{{\mbox{out}}}+2\times {F}_{{{\mbox{C}}}_{2}{{\mbox{H}}}_{4}}^{{\mbox{out}}}+2\times {F}_{{{\mbox{C}}}_{2}{{\mbox{H}}}_{6}}^{{\mbox{out}}}}{2\times {F}_{{{\mbox{C}}}_{2}{{\mbox{H}}}_{6}}^{{\mbox{in}}}}\times 100$$

(7)

$${{\mbox{Total}}}\,{{\mbox{Carbon}}}\,{{\mbox{balance}}}\,(\%)=\frac{{F}_{{\mbox{C}}{{\mbox{H}}}_{4}}^{{\mbox{out}}}+2\times {F}_{{{\mbox{C}}}_{2}{{\mbox{H}}}_{4}}^{{\mbox{out}}}+2\times {F}_{{{\mbox{C}}}_{2}{{\mbox{H}}}_{6}}^{{\mbox{out}}}+{F}_{{\mbox{CO}}}^{{\mbox{out}}}+{F}_{{\mbox{C}}{{\mbox{O}}}_{2}}^{{\mbox{out}}}}{2\times {F}_{{{\mbox{C}}}_{2}{{\mbox{H}}}_{6}}^{{\mbox{in}}}+{F}_{{\mbox{C}}{{\mbox{O}}}_{2}}^{{\mbox{in}}}}\times 100$$

(8)

where ${{F}_{x}}^{{{{\rm{in}}}}}$ and ${{F}_{x}}^{{{{\rm{out}}}}}$ represent the inlet and outlet flow rates of given species (mL min⁻¹), respectively. The weight hourly space velocity (WHSV, Eq. (9)), gaseous hourly space velocity (Eq. (10)) and C₂H₄ STY (Eq. (11)) were calculated as follows:

$${{\mbox{WHSV}}}\left({{\mbox{h}}}^{-1}\right)=\frac{{F}_{{{\mbox{C}}}_{2}{{\mbox{H}}}_{6}}^{{\mbox{in}}}\times {\rho }_{{{\mbox{C}}}_{2}{{\mbox{H}}}_{6}}}{1000\times {m}_{{\mbox{PtSn}}/{\mbox{Si}}{{\mbox{O}}}_{2}}}\times 60$$

(9)

$${{\mbox{GHSV}}}\left({\mbox{mL}}{{{\mbox{g}}}_{{\mbox{cat}}}}^{-1}{{\mbox{h}}}^{-1}\right)=\frac{{F}_{{{\mbox{C}}}_{2}{{\mbox{H}}}_{6}}^{{\mbox{in}}}+{F}_{{\mbox{C}}{{\mbox{O}}}_{2}}^{{\mbox{in}}}}{1000\times {m}_{{\mbox{PtSn}}/{\mbox{Si}}{{\mbox{O}}}_{2}}}\times 60$$

(10)

$${{\mbox{C}}}_{2}{{\mbox{H}}}_{4}{{\mbox{STY}}}\left({{\mbox{mol}}}\cdot {{{\mbox{g}}}_{{\mbox{metal}}}}^{-1}\cdot {{\mbox{h}}}^{-1}\right)=\frac{{F}_{{{\mbox{C}}}_{2}{{\mbox{H}}}_{4}}^{{\mbox{out}}}}{{1000{\mbox{V}}}_{{\mbox{m}}}\times {m}_{{\mbox{metal}}}}\times 60$$

(11)

where ${\rho }_{{{{{\rm{C}}}}}_{2}{{{{\rm{H}}}}}_{6}}$ is the density of ethane (1.356 g/L), ${m}_{{{{\rm{PtSn}}}}/{{{\rm{Si}}}}{{{{\rm{O}}}}}_{2}}$ is the mass of PtSn/SiO₂ (g), m_metal is the mass of active metal in the catalyst (g), V_m is the molar volume of gas (24.5 L mol⁻¹). The calculation equations related to the RWGS, PDH, and CO₂-ODHP were defined similarly to the CO₂-ODHE.

The deactivation constant (k_d) of the catalyst was defined using a first-order deactivation model¹⁷, based on the following Eq. (12):

$${{\mbox{k}}}_{{\mbox{d}}}\left({{\mbox{h}}}^{-1}\right)=\frac{{{{\mathrm{ln}}}}\left[\left(1-{X}_{{final}}\right)/{X}_{{final}}\right]-{{{\mathrm{ln}}}}\left[\left(1-{X}_{{initial}}\right)/{X}_{{initial}}\right]}{t}$$

(12)

Where X_final and X_initial represent the conversion measured at the initial and final periods of the experiment, t represents the reaction time (h), k_d is the deactivation rate constant (h⁻¹).

The kinetic experiments were conducted with the conversion of ethane and CO₂ controlled to be below 15% (well below the thermodynamic equilibrium at 600 °C), thus eliminating the effects of heat and mass transfer on the kinetic testing. The tandem catalyst loading was 20 mg (10 mg PtSn/SiO₂ + 10 mg CaCO₃). The ethane reaction order was tested by controlling the CO₂ flow rate at 10 mL/min, while the ethane flow rate (10.0, 9.6, 9.0, 8.6, 8.0 mL/min) was adjusted using Ar as the balance gas (total flow rate of 20 mL/min). The CO₂ reaction order was tested by controlling the ethane flow rate at 10 mL/min, while the CO₂ flow rate (10, 8, 6, 4, 2 mL/min) was adjusted using Ar as the balance gas (total flow rate of 20 mL/min). Arrhenius plots were tested in different temperature (570, 580, 590, 600 °C) under conditions where both ethane and CO₂ flow rates were 10 mL/min (total flow rate of 20 mL/min). The apparent activation energy (E_a) was calculated using the following Eq. (13):

$$k={{Ae}}^{-{E}_{{\mbox{a}}}/{\mbox{RT}}}$$

(13)

where k is the rate constant, A is the pre-exponential factor, and T is the temperature (K). E_a was obtained by fitting the values of ln(r) at different temperatures.

Catalyst regeneration

For the catalyst regeneration process, the reaction temperature was lowered to 500 °C, and the reactor was purged with Ar (50 mL/min) for 10 min to ensure the complete removal of ethane and CO₂. Then, 1 vol.% O₂/Ar (30 mL/min) was introduced for 30 min, followed by purging with Ar (50 mL/min) for 10 min to ensure the complete removal of O₂. Next, the gas was switched to 10 vol.% H₂/Ar (30 mL/min) as the temperature increased to 600 °C and maintained for 2 h. Finally, purge with Ar (50 mL/min) for 10 min to ensure the complete removal of H₂.

In situ XRD

In situ X-ray diffraction (In situ XRD) experiments were conducted on a 45 kV, 220 mA, and 9 kW Rigaku Smartlab using Cu Kα radiation filtered with graphite (λ = 1.5406 Å) and equipped with a high temperature cell. The powder samples of CaCO₃ + SiO₂ and PtSn/SiO₂ + CaCO₃ were separately loaded into high temperature cell vessels, and then purged with 10 vol.% H₂/Ar (20 mL/min) for 10 min. Firstly, an XRD pattern was recorded at room temperature. Then, the sample was heated at a rate of 20 °C/min under 10 vol.% H₂/Ar (20 mL/min) to 600 °C and maintained for 2 h. The XRD patterns were recorded immediately upon reaching 600 °C with 2θ range of 25–75° at a scan speed of 5°/min and at intervals of 15 min during the isothermal process. The in situ XRD experiments during the reaction process were conducted similarly. After treatment under 10 vol.% H₂/Ar (20 mL/min) for 2 h, the gas was switched to the reaction atmosphere (50 vol.% C₂H₆/CO₂), and XRD patterns were recorded.

XAS

X-ray absorption spectroscopy (XAS) spectra obtained at the BL14W beamline of the Shanghai Synchrotron Radiation Facility (SSRF). The storage rings at SSRF operated at 3.5 GeV with a stable current of 200 mA. Data was collected using a Si (111) double-crystal monochromator. The spectra of Pt L₃-edge and Sn K-edge were collected in transmission mode and fluorescence mode by Lytle detector, respectively at room temperature.

H₂-TPR and H₂-IMS

H₂ temperature-programmed reduction (H₂-TPR) and H₂ isothermal mass spectrometry (H₂-IMS) experiments were conducted on a chemical adsorption instrument (Micromeritics AutoChem II 2920) equipped with a mass spectrometer (HRP-20 EGA) at atmospheric pressure. The samples (0.1 g) of PtSn/SiO₂ + CaCO₃ or SiO₂ + CaCO₃ (mass ratio of 1:1) were separately loaded into U-shaped quartz tubes. For H₂-TPR testing process, the sample was pretreated with pure Ar (30 mL/min) at 150 °C for 1 h and cooled to 50 °C, followed by ramping the temperature at a rate of 10 °C/min from 50 °C to 850 °C in 10 vol.% H₂/Ar (30 mL/min). For H₂-IMS testing process, the sample was heated from room temperature to 600 °C at a ramp rate of 10 °C /min in pure Ar (30 mL/min) and stabilized for 10 min, then the gas was switched to 10 vol.% H₂/Ar (30 mL/min) and maintained at 600 °C for an additional 2 h. The exhaust gases were analyzed for signals of H₂ (m/z = 2), CO (m/z = 28), CO₂ (m/z = 44), and H₂O (m/z = 18) via mass spectrometer. Other temperature-programmed experiment details were showed in the supporting information.

In situ DRIFTS

In situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy was conducted on a Thermo Scientific Nicolet iS50 spectrometer, equipped with a high temperature cell featuring ZnSe windows and a liquid nitrogen-cooled detector. The catalyst powder was loaded into the center of the high temperature cell, and surface was leveled to minimize interference from reflections. The sample was initially heated to 600 °C in pure Ar (30 mL/min) flow and held for 0.5 h. Subsequently, background spectra were recorded under steady state conditions, followed the 10 vol.% C₂H₆/Ar (20 mL/min) was introduced into the high temperature reaction cell at 600 °C, with spectra recorded at intervals of one minute during this process.

DFT calculations

All DFT calculations were carried out utilizing the Materials Studio and the ultrasoft method. Details were shown in the supplementary.