Effect of Pd and Au on Hydrogen Abstraction and C–C Cleavage in Photoconversion of Glycerol: Beyond Charge Separation

Abstract

Photocatalytic conversion of polyols to value-added products is of great interest for the utilization of biomass as a chemical feedstock. Current research focuses on boosting the reaction rate and selectivity by employing metal nanoparticles (NPs) as charge separators and cocatalysts. However, the promotional role of metal NPs in such photocatalytic processes still remains unclear because of the lack of mechanistic understanding. Here, we have explored the role of supported Pd and Au NPs on TiO 2 in photocatalytic glycerol conversion under water-free, deaerated conditions by in situ spectroscopic methods. While the presence of Au NPs only results in partial conversion of glycerol at a low rate, Pd decoration promotes glycerol oxidation to a much higher conversion. In situ mass and vibrational spectrometry reveals that Pd/TiO 2 exhibits faster cleavage of O−H and C−H bonds in both glycerol and the derived intermediates as compared to Au/TiO 2 , thus leading to a higher glycerol conversion accompanied by the formation of additional molecular hydrogen. X-ray photoelectron spectroscopy suggests that the preferential adsorption of glycerol on the surface of Pd via hydroxyl groups results in an enhanced interfacial charge transfer, thus yielding a better photocatalytic activity.

Synergy of Pd atoms and oxygen vacancies on In2O3 for methane conversion under visible light

“…In a comparison, Au-In 2 O 3 and Pt-In 2 O 3 performed almost 100% over-oxidized products (HCHO), while with the trace yields of 1.4 and 0.9 μmol HCHO, respectively. Such difference was probably caused by the intrinsic characteristics of different noble metals, such as higher dehydrogenation capability of Pd than Au 49 , 50 . Meanwhile, Pt and Au-loaded catalysts seemed to over-oxidize of the major product CH 3 OH to HCHO as 100% selectivity of HCHO over the Pt and Au-loaded catalysts was observed.…”

Biomass components toward H2 and value-added products by sunlight-driven photocatalysis with electronically integrated Auδ−–TiO2: concurrent utilization of electrons and holes

“…The conversion of glycerol into VAPs is a point of attraction in the present era, as its under-utilization is posing a threat to the biodiesel industry; glycerol availability at a very low price should be exploited commercially. [9][10][11] Glycerol could be used in photocatalytic water splitting not only to increase H 2 production but also as a sacricial reagent to consume holes for partial oxidation to VAPs. [12][13][14][15] The same concept can be extended to other biomass components for their conversion to VAPs.…”

Highly selective oxidation of benzene to phenol with air at room temperature promoted by water

“…The surface of P25 has to be well-designed not only to provide active reaction sites but also to avoid over-oxidation of valuable chemicals. Metallic Pd was reported as an efficient catalytic site for benzene hydroxylation by thermal catalysis 2 , which could also enhance the charge separation 23 , 24 . Furthermore, isolated Cu species were reported as the active sites for benzene dissociation by forming copper-oxyl intermediates 25 , 26 .…”