Enhancing the understanding of the glycerol to lactic acid reaction mechanism over AuPt/TiO2 under alkaline conditions

Abstract

The oxidation of glycerol under alkaline conditions in the presence of a heterogeneous catalyst can be tailored to the formation of lactic acid; an important commodity chemical. Despite recent advances in this area, the mechanism for its formation is still a subject of contention. In this study, we use a model 1 wt.% AuPt/TiO2 catalyst to probe this mechanism through conducting a series of isotopic labelling experiments with 1,3-13 C glycerol. Optimisation of the reaction conditions was first conducted to ensure high selectivity to lactic acid in the isotopic labelling experiments. Selectivity to lactic acid increased with temperature and concentration of NaOH, but increasing the O2 pressure appeared to only influence rate of reaction. Using 1,3-13 C glycerol we demonstrate that conversion of pyruvaldehyde to lactic acid proceeds via a base-promoted 1,2-hydride shift, to produce lactic acid. There was no evidence to suggest that this occurs via a 2,1-methide shift under the conditions used in this study.

Highly active Ag/C nanoparticles containing ultra-low quantities of sub-surface Pt for the electrooxidation of glycerol in alkaline media

“…For example, the Cannizzaro reaction explain the absence of DHA in alkaline media and the formation of Lactate. [35,36] Other well-known equilibria in carbon hydrates chemistry is that between glucose and fructose [37] then we have proposed the equivalent equilibria between glyceraldehyde and DHA. Unfortunately, these reactions are several times not considered in many papers in the field of electrocatalysis, where the authors claim the J o u r n a l P r e -p r o o f electrochemical production of substances that several times are formed just by pure chemical steps.…”

Combined dehydrogenation of glycerol with catalytic transfer hydrogenation of H2 acceptors to chemicals: Opportunities and challenges

“…Selective oxidation of glycerol has been demonstrated to be thermodynamically more favorable for C–H bond activation under mild reaction conditions (e.g., lower operating temperature and alkali concentration), which greatly reduces energy consumption ( Shen et al, 2010 ; Lakshmanan et al, 2013 ; Tao et al, 2017 ; Evans et al, 2020 ; Tao et al, 2020 ; Torres et al, 2021 ). Furthermore, low reaction temperature can also significantly inhibit C–C bond cleavage by alkalis, thus good selectivity of C 3 products.…”

“…Furthermore, low reaction temperature can also significantly inhibit C–C bond cleavage by alkalis, thus good selectivity of C 3 products. Selective oxidation of glycerol to LA is generally carried out with the promotion of various noble metal and some non-noble metal catalysts (e.g., Au, Pt, Pd, and polyoxometalate ) ( Shen et al, 2010 ; Lakshmanan et al, 2013 ; Xu et al, 2013 ; Cho et al, 2014 ; Purushothaman et al, 2014 ; Zhang et al, 2016a ; Zhang et al, 2016b ; Arcanjo et al, 2017 ; Tao et al, 2017 ; Zhang et al, 2017 ; Douthwaite et al, 2020 ; Evans et al, 2020 ; Tao et al, 2020 ; Torres et al, 2021 ; Wang et al, 2021 ). In the first important advances, Shen et al (2010) reported that the bimetallic Au–Pt catalysts exhibit excellent performances with a high yield of 86% in the presence of alkali and O 2 at 90°C.…”

“…Despite fast progress in this research field, the mechanism for the formation of LA is still a subject of contention, especially the competitive pathway in dehydration of glyceraldehyde and C–C bond cleavage as well as the nature of rearrangement reaction. Recently, Evans et al (2020) thoroughly studied the formation mechanism of LA from glycerol by conducting a series of isotopic labeling experiments with 1.3– 13 C glycerol using a model AuPt/TiO 2 catalyst. The reaction conditions, including reaction temperature, pH, and O 2 pressure, are highly influential on both the conversion rate of glycerol and product distribution ( Scheme 2A ).…”

Recent Advances in Glycerol Catalytic Valorization: A Review

“…The reaction is commonly described in the literature under basic conditions, mainly due to the fact that alkaline media accelerates the reaction, improves the selectivity to C3 products, and prevents deactivation [183]. Recent advances in the employment of noble metals as active phases, especially Au and Pt, are focused on selective oxidation base-free and room condition reactions [29,[184][185][186][187]. In this line, support properties may be key to achieving this objective through metal particle sintering prevention [188], as well as the establishment of metal synergies with superficial acid-base centers [189].…”