Extended Data Fig. 7: Additional DRIFTS and solid-state NMR analysis.
From: Promoting active site renewal in heterogeneous olefin metathesis catalysts
a, Low temperature chemisorption of various olefins on spent 3%SOMC: (i) ethylene, (ii) propylene (presented in the main text but reproduced here for ease of comparison), (iii) 2-butene, (iv) propylene + 4ME, (v) propylene + i4ME. The spectrum of an activated blank catalyst (black) was obtained with respect to the KBr background. Vertical offsets were applied for clarity. Isobutene was omitted from the series because it oligomerized into a non-volatile oily phase. The fact that the peaks in (iv) and (v) (4ME and i4ME) differ only in intensity but not position is consistent with a common chemisorbed species but different thermodynamics of protonation. b, Solid-state 2D 1H{13C} D-HMQC NMR correlation spectra of 3%SOMC reacted with propylene without i4ME. The spectra were acquired at 9.4 T, 298 K, 40 kHz MAS, and with dipolar recoupling periods of 18 rotor periods (0.45 ms, red) or 60 rotor periods (1.5 ms, black). The 1D 13C projections of the two 2D spectra are shown along the ordinate, and a 1D 1H echo spectrum acquired under the same conditions is shown for comparison. The short (red) and long (black) recoupling times appear to select for -CH3 and -CH2- signals respectively, and the overall signals are consistent with predominantly alkyl species. Notably, the alkoxide signals of Fig. 3b are absent, likely below the detection limit of solid-state NMR. c, Comparison of the solid-state 1D 1H MAS NMR spectra of 3%SOMC after reaction with (top) propylene without i4ME or (bottom) propylene with i4ME. The signals are generally similar but with very different relative intensities indicating different distributions of the corresponding surface species. Specifically, reaction with propylene alone appears to result in larger relative quantities of surface-bound aromatic and/or olefinic species (1H signals from 4.5–8 ppm), while reaction with i4ME appears to favor greater relative proportions of surface alkoxide and alkyl moieties. The spectra were acquired at 9.4 T, 298 K, 40 kHz MAS, and with rotor synchronized echo delays rotor periods of 2 rotor periods (0.05 ms).
