Detailed Kinetic Investigations on the Selective Oxidation of Biomass to Formic Acid (OxFA Process) Using Model Substrates and Real Biomass

Abstract

A detailed kinetic analysis of the selective catalytic oxidation of different biogenic model substrates to formic acid (OxFA process) is presented using two different polyoxometalate catalysts, HPA-2 (H 5 PV 2 Mo 10 O 40 ) and HPA-5 (H 8 PV 5 Mo 7 O 40 ). By using high oxygen pressures (30−60 bar) and temperatures of 80−90 °C in aqueous solution, we were able to investigate the rate-determining substrate oxidation step catalyzed by the oxidized form of the polyoxometalates (POMs) by keeping the concentration of the catalytic active species constant. Under these conditions, kinetic parameters like effective reaction order and reaction rate constants could be determined by the differential method for model substrates like glucose, fructose, sorbitol, and gluconic acid. Furthermore, kinetic experiments using the two different catalysts showed a different behavior for various functionalities within the carbon framework of the substrate with the tendency of higher reaction rates with the HPA-5 catalyst. This effect was more pronounced for disaccharides like cellobiose and sucrose than for monosaccharides. Finally, a detailed kinetic study for water-insoluble biomasses like beech and spruce wood showed differences in formic acid (FA) formation and product selectivities depending on the composition of the wood in terms of their ratios of lignin, cellulose, and hemicellulose.

Combining autoclave and LCWM reactor studies to shed light on the kinetics of glucose oxidation catalyzed by doped molybdenum-based heteropoly acids

“…1), was suppressed by applying oxygen pressures of 60 bar, where the catalyst reoxidation was shown to be much faster than the substrate oxidation. 21 To obtain further insight into the kinetics of the oxidation step r 1 samples were taken from the autoclave during the rst 4 h. For the determination of the effective activation energies, the experiments were performed at different reaction temperatures (120 C, 140 C and 160 C). The liquid product distribution during the experiments is exemplarily shown for the catalyst HPA-Nb in Fig.…”

“…for the two vanadium-substituted POMs H 5 PV 2 Mo 10 O 40 (HPA-2) and H 8 PV 5 Mo 7 O 40 (HPA-5) the oxidation kinetics of monosaccharides like glucose, fructose, sorbitol, and gluconic acid as well as disaccharides like cellobiose and sucrose, up to waterinsoluble biomass like beech and spruce wood were determined. 21 Moreover, Yokoyama et al performed kinetic studies on the oxidation of non-phenolic lignin subunits by tungstenbased Keggin-POMs in water. 22 Besides, these autoclave studies, which allow to operate close to a later on technical system, employing micro-scale reactors for kinetic studies can show signicant advantages.…”

Catalytic Transformation of Cellulose and Its Derivatives into Functionalized Organic Acids

“…Keggin‐type polyoxometalates, in particular, vanadium‐containing H 5 PVMo 11 O 40 , H 5 PV 2 Mo 10 O 40 , and H 8 PV 5 Mo 7 O 40 , have recently demonstrated high performances for the oxidative conversion of cellulose and related carbohydrates into formic acid by using molecular oxygen as oxidant. Wasserscheid and co‐workers studied H 5 PV 2 Mo 10 O 40 ‐catalyzed glucose conversion in water .…”

Utilization of a Hydrogen Source from Renewable Lignocellulosic Biomass for Hydrogenation of Nitroarenes

“…And for the hydrolysis‐oxidation of complex biomass of cellulose, the FA yields always were obtained below 70 % . Other promising catalyst systems for the extremely demanding raw biomass hydrolysis‐oxidation, such as HPA‐5 (H 8 PV 5 Mo 7 O 40 ) in the presence of p‐ TSA ( para ‐toluenesulfonic acid) and 1‐hexanol, HPA‐5 promoted with HCl, and VOSO 4 in the presence of EtOH, were investigated for the FA production . Our developed 1 v% DMSO promoted NaVO 3 /H 2 SO 4 hydrolysis–oxidation catalysis system displayed the best FA yield .…”

“…[17] For the oxidation of primary biomass of glucose or saccharides, up to 85 % yields FA or formate was obtained. [18] However, large amount of 1-hexanol (100 g of 1-hexanol/1.80 g glucose) or excessive NaOH with more than stoichiometric H 2 O 2 were required. [18c,d] And for the hydrolysis-oxidation of complex biomass of cellulose, the FA yields always were obtained below 70 %.…”