Fig. 3: Optimization of Cu(x)Ca(1-x)O MMO catalyst composition and reaction conditions.
A Probe reaction yield (1,4-BDO conversion to γ-butyrolactone) dependence on open-system (i.e., semi-batch) vs. closed-system (i.e., batch) experiments. B Lactone yields at 180 °C, 24 h, diol/catalyst mass ratio 20 g/g. The shades of burgundy represent Cu(x)Ca(1-x)O MMO catalysts where darker shades imply higher Cu-content, while the green datapoints represent the reference compounds like CuO and Cu powder. The pink data points (bulk compounds CaO and Ca(OH)2) are not shown due to the log-scale x-axis and are indicated with an arrow instead. Error bars are standard deviations of n = 3–15 replicates, and when not visible are hidden behind the data point. C The lactone yield data are used to calculate a nominal STY by normalizing by moles of Cu. D STY as a function of lactone yield. E Catalyst mass-normalized rates used for Koros-Nowak /Madon–Boudart test, showing that as Cu-content increases, the reaction rate increases non-linearly (i.e rate ∝ [Cu]0.5). F Arrhenius plot estimating apparent activation barriers for 1,4-BDO, 1,4-PDO, and 1,5-PDO converting to corresponding lactones over Cu(0.05)Ca(0.95)O MMO catalyst, 500 rpm stirring rate, diol/catalyst mass ratio: 20 g/g. All numerical data shown in this figure are provided in supplementary data tables.
