Rational Design of Metal Oxide Solid Acids for Sugar Conversion

Abstract

Aqueous-phase acid-catalyzed reactions are essential for the conversion of cellulose-based biomass into chemicals. Brønsted acid and Lewis acid play important roles for these reactions, including hydrolysis of saccharides, isomerization and epimerization of aldoses, conversion of d-glucose into 5-hydroxymethylfurfural, cyclodehydration of sugar alcohols and conversion of trioses into lactic acid. A variety of metal oxide solid acids has been developed and applied for the conversion of sugars so far. The catalytic activity is mainly dependent on the structures and types of solid acids. Amorphous metal oxides possess coordinatively unsaturated metal sites that function as Lewis acid sites while some crystal metal oxides have strong Brønsted acid sites. This review introduces several types of metal oxide solid acids, such as layered metal oxides, metal oxide nanosheet aggregates, mesoporous metal oxides, amorphous metal oxides and supported metal oxides for sugar conversions.

Lepidocrocite-Type Layered Titanate Nanoparticles as Photocatalysts for H2 Production

“…Layered transition metal oxides (e.g., layered titanates and niobates) consisting of transition metal oxide nanolayers and interlayer exchangeable cations have been widely used for designing green materials/devices such as adsorbents, − solid acid catalysts, − lithium (sodium)-ion batteries − electrocatalysts, photocatalysts, ,,− and dye-sensitized solar cells. − The compositional variations, combined with the ability to accommodate various guest species in the interlayer space, make layered transition metal oxides more attractive. Transition metal oxide nanosheets obtained by exfoliation of the parent layered compounds have attracted attention from both scientific and practical viewpoints owing to their unique physicochemical properties based on the highly anisotropic shape associated with the large accessible surface area. − Aggregation of 2D nanosheets and positively charged species obtained by electrostatic interactions have been used to obtain porous hybrids, − which are useful due to their easily accessible pores for reactants and functional units such as dye sensitizers when compared with well-ordered (densely packed) intercalation compounds.…”

Multi-Step Exploitation of Raw Arundo donax L. for the Selective Synthesis of Second-Generation Sugars by Chemical and Biological Route

“…For this reason, Arundo donax L. is widely used as a substrate for the synthesis of important platform-chemicals, biofuels, and second-generation sugars [14,16,25,27,35,[46][47][48]. In particular, the interest towards the synthesis of xylose and glucose is continuously growing, due to their promising applications in both chemical and biological processes to produce alcohols, acids, oils, hydrocarbons, hydrogen, and other valuable products [1,15,22,34,46,47,[49][50][51][52][53][54][55]. However, up to now, only a few works discussed the employment of acid solid catalysts for the conversion of Arundo donax L. to value-added products, performing the reaction in the presence of ionic liquids as solvents, which have some criticisms related to their high viscosity, toxicity and cost, which strongly limit the sustainability of this approach.…”

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

“…Acid catalyst is one type of the most important catalysts widely used in the chemical industry. In comparison with the liquid acid catalysts, solid acids, as noncorrosive, separable, reusable, and environmentally benign catalysts, have attracted tremendous attention in esterification, hydration/dehydration, hydrogenation/dehydrogenation, redox reactions, and so on. − In many catalytic reactions, water molecules exist as reactant, product, or solvent, which may affect the acidity and stability of some solid acid catalysts . It is well understood that a Brønsted acid site is usually not easy to connect with a water molecule and to change its acidity, however, the metallic center of a Lewis acid site has a much stronger affinity to a water molecule, thus, provoking the partial decrease of Lewis acidity in the presence of water .…”