Overcoming the limitations of gold catalysts in hydrogenation: enhanced activity with full hydrogen utilization

Abstract

Application of nano-scale supported Au in catalytic hydrogenation delivers high chemoselectivity but low activity using (pressurized) H 2 far in excess of stoichiometric requirements. We have tackled the issues of low reaction rate and inefficient hydrogen utilization through a series of approaches taking Au/CeO 2 (mean Au size = 2.8 nm) as a test catalyst. Increased spillover hydrogen (using physical mixtures of Au/CeO 2 with CeO 2 and SiO 2 ) and the promotional effect of water (via catalytic dissociation on surface oxygen vacancies) resulted in a fourfold increase in the selective rate of furfural hydrogenation to furfuryl alcohol. In contrast, Pd/CeO 2 and Ni/CeO 2 promoted decarbonylation (to furan), hydrogenolysis (to 2-methylfuran) and ring reduction (to tetrahydrofurfuryl alcohol). Coupling (2-butanol ? 2-butanone) dehydrogenation over Cu/SiO 2 (mean Cu size = 7.8 nm) with furfural hydrogenation over Au/CeO 2 further increased rate with full utilization of the hydrogen generated in dehydrogenation. The coupling strategy allows ''hydrogen free'' hydrogenation that circumvents the limitation of Au in standard catalytic hydrogenation. This can open new avenues to exploit the ultra-selectivity of Au for continuous production of high value commodity products.

Gas Phase Hydrogenation of Furaldehydes via Coupling with Alcohol Dehydrogenation over Ceria Supported Au-Cu

“…Full hydrogen utilisation was achieved in the coupled system with all the amount generated via 2-butanol dehydrogenation being utilised in HMF hydrogenation, i.e., H 2 /HMF = 1. We recorded no conversion in the stand-alone dehydrogenation of 2-butanol (in N 2 ) over Au/CeO 2 while under similar reaction conditions ( P = 1 atm; T = 498 K) Cu/SiO 2 delivers negligible activity in the gas phase hydrogenation of furfural [ 29 ]. This suggests that Cu and Au are the active sites for 2-butanol dehydrogenation and HMF hydrogenation, respectively.…”

Hydrogen Spillover‐Enhanced Heterogeneously Catalyzed Hydrodeoxygenation for Biomass Upgrading

“…Furthermore, since most of the HDO reactions occur under liquid conditions, it is important to understand the impact of the solvent on the HDO reaction as well as the hydrogen spillover. Au catalysts were used for furfural hydrogenation to obtain high selectivity and low reaction rates, while Au/CeO 2 could promote C=O selective hydrogenation, [60] resulting in a fourfold increase in the selectivity of furfural hydrogenation to furfuryl alcohol and increasing the hydrogenation rate from 26 to 31 mol furfural mol Au −1 h −1 , [61] which was attributed to the spillover of active hydrogen dissociated at Au metal position to CeO 2 support surface, and the spillover hydrogen contributed to improving hydrogenation activity [34a] . The effect of adding water to the furfural feedstock was tested on Au/CeO 2 , with a threefold increase in the hydrogenation rate of furfural at H 2 O/furfural=0.2–1.…”

Heterolytic bond activation at gold: evidence for gold(iii) H–B, H–Si complexes, H–H and H–C cleavage

“… 4 , 5 There are significant differences, however, not least in the distinct reluctance of gold to undergo oxidative addition reactions, 6 , 7 and an experiment-based outline of the reactivity of gold, and in particular of the much less well explored chemistry of gold( iii ), is only now beginning to emerge. 8 – 10 Heterogeneous gold catalysts show high activity in a multitude of reactions, for example in hydrogenations, 11 – 16 including the hydrogenation of nitro compounds 17 – 19 and hydrogen transfer, 20 in acetylene hydrochlorination, 21 in the water–gas shift reaction, 22 in hydrosilylations and in catalytic dehydrogenative Si–O coupling reactions. 23 – 28 Similarly, homogeneously gold-catalyzed hydrogenations and hydrosilylations 29 – 31 as well as alkyne hydroborations 32 have been reported.…”