Effect of support redox character on catalytic performance in the gas phase hydrogenation of benzaldehyde and nitrobenzene over supported gold

Abstract

A range of oxides (γ-Al2O3, TiO2, ZrO2, CeO2, α-Fe2O3 and Fe3O4) with different redox properties were used to support nano-scale (mean = 2-8 nm) Au and employed in the gas phase hydrogenation of benzaldehyde and nitrobenzene. The catalysts were subjected to TPR, H2/O2 titration, H2 TPD, XRD, TEM/STEM and XPS analysis. The supported Au phase promoted partial reduction of the reducible supports through the action of spillover hydrogen (based on TPD), which generated surface oxygen vacancies (demonstrated by O2 titration) that inhibit Au particle sintering during catalyst activation. Electron transfer to generate charged Au species (determined by XPS) correlates with support ionisation potential. Higher nitrobenzene hydrogenation (to aniline) TOFs were recorded relative to benzaldehyde where rate increased with decreasing Au size (from 8 to 4 nm) with measurably lower TOF over Au <3 nm. Strong binding of-CH=O and-NO2 functions to oxygen vacancies resulted in lower hydrogenation rates. Higher temperatures (>413 K) promoted benzaldehyde hydrogenolysis to toluene and benzene. The formation of Au δon non-reducible Al2O3 favoured selective reduction of-CH=O with full selectivity to benzyl alcohol at 413 K.

The Promoting Effect of Ce on the Performance of Au/CexZr1−xO2 for γ-Valerolactone Production from Biomass-Based Levulinic Acid and Formic Acid

“…The other involves that the reduced Au can further adsorb H 2 and spill more hydrogen species over the support to reduce Ce 4+ . This result is well consistent with that in literature [48], which indicates that the supported Au could promote the reduction of Ce 4+ . Moreover, it is also pointed out that the reduction of the reducible supports (e.g., Ce 4+ ) could contribute to inhibit sintering of Au particle in the process of catalyst activation.…”

Structure and Reactivity of Cu-doped Au(111) Surfaces

“…Moreover, supported gold catalytic systems can also operate as highly selective catalysts for the hydrogenation of important feedstocks such as benzaldehyde [73] and nitrobenzene [74]. An impediment to the use of gold for this type of catalytic chemistry is the high activation barrier for H 2 dissociative adsorption which limits the rate of hydrogenation and necessitates the use of undesirably high H 2 pressures.…”

Gas phase selective hydrogenation of phenylacetylene to styrene over Au/Al2O3

“…There is considerable scope to enhance Au promoted styrene production in continuous operation. In previous work, we have demonstrated 100% selectivity in the hydrogenation of functionalised nitroarenes over oxide supported Au to target amine products and in the conversion of benzaldehyde to benzyl alcohol . We have now extended that work to consider the catalytic action of Au/Al 2 O 3 in selective phenylacetylene to styrene conversion, assessing the effects of temperature and H 2 partial pressure as critical process variables.…”

“…In previous work, we have demonstrated 100% selectivity in the hydrogenation of functionalised nitroarenes over oxide supported Au to target amine products [20][21][22] and in the conversion of benzaldehyde to benzyl alcohol. 23 We have now extended that work to consider the catalytic action of Au/Al 2 O 3 in selective phenylacetylene to styrene conversion, assessing the effects of temperature and H 2 partial pressure as critical process variables. Drawing on the published liquid phase catalytic work where supported Pd was the predominant catalyst system, 4,6,[24][25][26][27] we have employed Pd/Al 2 O 3 as benchmark and correlate catalyst testing with structural characterisation.…”