Kinetic modeling of Pt/C catalyzed aqueous phase glycerol conversion with in situ formed hydrogen

Abstract

Detailed kinetic modeling of Pt/C catalyzed conversion of glycerol to lactic acid, glycols, and alcohols with in situ formed hydrogen is reported. Experimental concentration-time profiles were obtained in a batch slurry reactor at different glycerol concentrations, nitrogen partial pressures, and NaOH concentrations in a temperature range of 130-1608C. Six different kinetic models were evaluated to describe the competing dehydrogenation, hydrogenolysis, dehydration, and CAC cleavage reactions, and discriminated to fit the experimental data. It is found that a "dual-similar-site" mechanism involving alkali promoted dehydrogenation, on two adjacent Pt sites to affect CAC and CAO cleavage best describes the experimental data. The dehydrogenation reaction proceeds with a significantly lower activation barrier (E a 5 53 kJ/mol) compared with the noncatalytic hydrothermal conversion (E a 5 128 kJ/mol). The activation energy for glycerol hydrogenolysis on Pt/C catalyst without adding hydrogen is estimated to be 64 kJ/mol. a Rate/adsorption constants with 95% confidence level b Rate constant unit: m 3 /kg cat.h. c Unit of E a and DH: kJ/mol. d Sensitivity analysis procedures in Supporting Information Table S4-1, unit: kJ/mol. Scheme 6. Energy diagram of tandem catalysis vs. hydrothermal and conventional hydrogenolysis reactions (left: hydrothermal conversion vs. catalytic dehydrogenation; right: hydrogenolysis with external H 2 vs. with in situ H 2 ).

Catalytic Transfer Hydrogenation of Biomass‐Derived Substrates to Value‐Added Chemicals on Dual‐Function Catalysts: Opportunities and Challenges

“…Both computational and experimental results have shown that dehydrogenation, although thermodynamically unfavorable, is kinetically favorable on metal catalysts . Hydrogenolysis or hydrogenation, on the other hand, seem to follow a different path to that of APH under a H 2 environment.…”

Nanostructured Metal Catalysts for Selective Hydrogenation and Oxidation of Cellulosic Biomass to Chemicals

“…Magnetic Pd/Fe 3 O 4 nanocatalysts were designed for selective oxidation of hydroxymethylfurfural to furan dicarboxylic acid (involving oxidation of C=O and C−OH groups), as shown in Figure (e) . Pt (111) surface has also been shown to display bi‐functional properties in polyol hydrogenolysis with in‐situ formed hydrogen (by dehydrogenation) without the need for adding external hydrogen …”

“…Various metal catalysts show promising performances in hydrogenolysis of polyols to 1,2‐PDO, including Pt, Ru, Cu, Ni, among which Ru and Cu catalysts are most extensively studied with promising performances. This is because Ru‐based catalysts show remarkable activity while Cu catalysts often exhibit high selectivity towards 1,2‐PDO.…”

“…reforming, water gas shift and dehydrogenation) reactions can be incorporated with hydrogenolysis in a one pot process to produce glycols and other valuable co‐products such as LA and alcohols without using external hydrogen . One conversion route involves sacrificing small fraction of polyol to generate H 2 while remaining substrate is converted on bifunctional catalyst surface with H 2 formed in‐situ . In another approach, formic acid, 2‐propanol, etc as liquid H 2 precursors are used to conduct hydrogenolysis reaction on bifunctional catalyst surface .…”

“…In another study, we observed that dehydrogenation reaction generates glyceraldehyde as an intermediate, which undergoes sequential reactions to form LA, while H 2 formed in‐situ reacts with remaining feedstocks to form glycols and alcohols. The overall carbon selectivity is as high as 95+% (Figure , entry#4 in Table ) . Rh (111) catalyst displays similar synergy in converting glycerol under inert atmosphere (entry#5 in Table ) .…”