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Glycerol Selective Oxidation to Lactic Acid over AuPt Nanoparticles; Enhancing Reaction Selectivity and Understanding by Support Modification
Author(s) -
Douthwaite Mark,
Powell Natasha,
Taylor Aoife,
Ford Grayson,
López José Manuel,
Solsona Benjamin,
Yang Nating,
SanahujaParejo Olga,
He Qian,
Morgan David J.,
Garcia Tomas,
Taylor Stuart H.
Publication year - 2020
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.202000026
Subject(s) - catalysis , selectivity , lactic acid , anatase , chemistry , mesoporous material , x ray photoelectron spectroscopy , inorganic chemistry , chemical engineering , materials science , organic chemistry , photocatalysis , biology , bacteria , genetics , engineering
A high surface area mesoporous TiO 2 material (110 m 2 /g) was synthesised using a nanocasting methodology, utilizing SBA‐15 as a hard template. This material was subsequently used as a support to prepare a series of 1 wt.% AuPt/TiO 2 catalysts, synthesised by conventional impregnation and sol‐immobilisation. Catalysts were tested for the oxidation of glycerol to lactic acid and their performance was compared with corresponding catalysts supported on TiO 2 −P25, TiO 2 ‐anatase and TiO 2 ‐rutile. Higher rates of reaction and higher selectivity to lactic acid were observed over nanocast TiO 2 supported catalysts. The increased performance of these catalysts was attributed to the presence of Si on the surface of the support, which likely arose from inefficient etching of the SBA‐15 template. The presence of Si in these catalysts was confirmed by X‐ray photoelectron spectroscopy and electron energy loss spectroscopy. It was proposed that the residual Si present increases the Brønsted acidity of the TiO 2 support, which can lead to the formation of Lewis acid sites under reaction conditions; both sites are known to catalyse the dehydration of a primary alcohol in glycerol. Typically, under alkaline conditions, lactic acid is formed by the nucleophilic abstraction of a hydrogen. Thus, we propose that the improved selectivity to lactic acid over the nanocast TiO 2 supported catalyst is attributed to the co‐operation of heterogeneous and homogeneous dehydration reactions, as both compete directly with a direct oxidation pathway, which leads to the formation of oxidation products such as glyceric and tartronic acid.