Dehydration of sugars to 5-hydroxymethylfurfural and non-stoichiometric formic and levulinic acids over mesoporous Ta and Ta-W oxide solid acid catalysts

Supported MoOx and WOx Solid Acids for Biomass Valorization: Interplay of Coordination Chemistry, Acidity, and Catalysis

“…A higher percentage of Brønsted to Lewis acid sites is favorable for achieving higher sugar conversion and HMF selectivity, as noticed over mesoporous Ta−W oxides. 232 The reason is that the second step, i.e., dehydration of fructose to HMF, is strongly catalyzed by Brønsted acid sites. So, the consumption of fructose will induce the isomerization step.…”

“…Conversion of glucose to value-added products (e.g., HMF) via fructose formation requires both Brønsted and Lewis acid sites, but a higher percentage of Brønsted to Lewis acid sites is favorable for improved HMF formation because Brønsted acid sites efficiently catalyze the fructose-to-HMF dehydration step that eventually increases glucose conversion by inducing the glucose-to-fructose isomerization step. 232 The excellent synergistic effect of acid sites of supported MoO x and WO x catalysts with redox metals is beneficial for the hydroprocessing of sugars and their furan derivatives. Interestingly, there is no role of Brønsted acid sites in Pd−WO x /Al 2 O 3 for the hydroprocessing of glucose to produce 1,2-propanediol.…”

Sugar dehydration to 5-hydroxymethylfurfural in mixtures of water/[Bmim]Cl catalyzed by iron sulfate

“…10 Besides, HMF can be used to synthesize 2,5-furandicarboxylic acid, a promising monomer for the manufacture of bio-based polyethylene furanoate (with better mechanical strength and oxygen/CO2 barrier properties) to replace the petroleum-based polyethylene terephthalate. 11 In the past decades, numerous research efforts have been devoted to converting bio-based carbohydrates into HMF in various catalytic reaction systems, such as the use of catalysts (including among others mineral acid, 12,13 metal salts 14 and solid acid catalysts like HfO(PO4)2, 15 activated carbon, 16 zeolite, 17 TiO2, 18 Ta-W oxide 19 and novel mesoporous carbon 20 ), and the use of water or other organic solvents, 21,22 aqueous-organic biphasic solvent system 18,23,24 as well as sub-or supercritical systems. 25,26 Fructose, derived from the hydrolysis of biomass (rich in the cellulosic component), 27,28 is considered as a preferred starting feedstock for HMF synthesis since the furanic structures thereof make it easier to be converted with a higher selectivity towards HMF as compared to raw biomass.…”

Effect of Adsorbed Water Molecules on the Surface Acidity of Niobium and Tantalum Oxides Studied by MAS NMR

“…To gain a deep understanding of the water–surface interactions, it is vital to consider the structural models of Lewis and Brønsted acid sites on Nb 2 O 5 · n H 2 O and Ta 2 O 5 · n H 2 O. The large ion radius of Nb 5+ or Ta 5+ makes it difficult to form a tetrahedral structure with oxygen ions, hence, the main components of niobic/tantalic acid and amorphous niobium/tantalum pentoxide are distorted MO 6 octahedra, while small amounts of MO 4 , MO 5 , MO 7 , and MO 8 also exist. − As shown in Figure , due to the oxygen atoms in the different ways of sharing edges and corners, the hydroxyl groups on distorted MO 6 octahedra exhibit Brønsted acidity, while the highly distorted MO 6 octahedra exhibit weak Lewis acidity, and a small amount of MO 4 and MO 5 shows strong Lewis acidity. ,, As mentioned herein before, the contents of low coordinated MO 4 and MO 5 structural units as well as highly distorted MO 6 decrease with increasing calcination temperature, leading to the increased regularity and coordination of the structural units. As a result, the MO 4 and MO 5 structural units of Nb 2 O 5 -350 and Ta 2 O 5 -350 are less than that of Nb 2 O 5 · n H 2 O and Ta 2 O 5 · n H 2 O, and the structural units of Nb 2 O 5 -450 and Ta 2 O 5 -450 are mainly MO 6 along with some MO 5 units.…”