Exploiting basic principles to control the selectivity of the vapor phase catalytic oxidative cross-coupling of primary alcohols over nanoporous gold catalysts

Abstract

Achieving high selectivity for high volume chemical synthesis is important for lowering energy consumption through reduction in waste. We report the selective synthesis of methyl estersmethyl acetate and methyl butyrate-through catalytic O 2-assisted cross-coupling of methanol with ethanol or 1-butanol using activated, support-free nanoporous gold (npAu). Both wellcontrolled studies on ingots in UHV and experiments under ambient pressure catalytic conditions on both ingots and microspherical hollow shell catalysts reveal guiding principles for controlling selectivity. Under UHV conditions the ester products of the cross-coupling of methanol with both ethanol and 1-butanol evolve near room temperature in temperature programmed reaction studies, indicating that the reactions occur facilely. Under steady-state catalytic operation high, stable activity was observed for cross-coupling in flowing gaseous reactant mixtures at atmospheric pressure and 423 K with negligible combustion. Optimum selectivity for cross

Catalyst design for enhanced sustainability through fundamental surface chemistry

“…Remarkably, the trends in selectivity over different alcohol ratios are not only the same between Au(111) and npAg 0.03 Au 0.97 under low-pressure conditions, but they also match the activity of ozone-treated npAg 0.03 Au 0.97 materials under catalytic conditions [52]. This correspondence is possible because the alcohols are only activated on the surface when adsorbed O is present, which prevents the accumulation of spectator species at atmospheric pressure.…”

“…There is also no formation of ethyl formate or butyl formate. However, acetaldehyde is generated under catalytic conditions, while it is not observed at low pressure [19,52]. At higher methanol mole fractions, ester production predominates, as was observed in surface science experiments.…”

“…At an 85 : 15 ratio of methanol to ethanol, methyl acetate makes up 59% of the ester yield, ethyl acetate 32% and methyl formate 9% [52]. Esters account for 90% of the overall yield, with CO 2 as the residual product, and a possible trace of acetaldehyde.…”

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“…Only esters and acetaldehyde were produced; no CO 2 was detected. The product distributions measured as a function of methanol mole fraction showed that excess methanol (≈80 %) is required for maximum production of methyl acetate, similar to npAu under similar conditions . The selectivity for acetaldehyde production decreased both as the total alcohol concentration increased from 2 to 10 % and as the temperature was increased up to 240 °C (Figure S10), also analogous to npAu .…”

“…The product distributions measured as a function of methanol mole fraction showed that excess methanol (≈80 %) is required for maximum production of methyl acetate, similar to npAu under similar conditions . The selectivity for acetaldehyde production decreased both as the total alcohol concentration increased from 2 to 10 % and as the temperature was increased up to 240 °C (Figure S10), also analogous to npAu . There are, though, differences between the CTP and nanoporous catalysts: The CTP‐Ag 10 Au 90 produced significantly more acetaldehyde and the rate of ethanol conversion was three to four times higher for the CTP SiO 2 –Ag 10 Au 90 catalyst (0.018 mmol g −1 s −1 ) than for npAu under the same conditions (0.004 mmol g −1 s −1 , Table S2).…”