Single-Step Formation of Metal Oxide Nanostructures Wrapped in Mesoporous Silica and Silica–Niobia Catalysts for the Condensation of Furfural with Acetone

Abstract

The integration of metal oxide nanomaterials with mesoporous silica is a promising approach to exploiting the advantages of both types of materials. Traditional synthesis methods typically require multiple steps. This work instead presents a fast, one-step, template-free method for the synthesis of metal oxides homogeneously dispersed within mesoporous silica, including oxides of W, Ti, Nb, Ta, Sn, and Mo. These composites have tunable metal oxide contents, large surface areas, and wide mesopores. The combination of Nb2O5 nanoparticles (NPs) with SiO2 results in an increased surface area and a larger number of acid sites compared to pure Nb2O5 NPs. The surface texture and acidity of the silica–niobia composites can be tuned by adjusting the Nb/Si molar ratio. Moreover, the silica provides protection to the niobia NPs, preventing sintering during thermal treatment at 400 °C. The silica–niobia materials exhibit superior performance as catalysts in the aldol condensation of furfural (Fur) with acetone compared to pure niobia, leading to an up to 62% in product yield. Additionally, these catalysts show remarkable stability, retaining their performance over multiple runs. This work demonstrates the potential of the proposed synthesis approach for preparing more sustainable, high-performance, durable, and stable nanoscale metal oxide-based catalysts with a tunable composition, surface area, and active site density.

Chemical valorisation of biomass derived furanics and carboxylic acids over niobium-based catalysts

“…Simply, acetophenone as the reaction solvent plus the metal precursors (silicon tetrachloride and niobium( v ) chloride) in the desired amounts, were subjected to microwave heating at 220 °C for 20 min. 61 The materials were used in the catalytic reactions without calcination (only washing with acetone and ethanol, and drying at 65 °C; samples denoted as SiNb x -NC) or after calcination at 400 °C (air, 5 h, 1 °C min −1 ; samples denoted as SiNb x ). 61 In the sample names, x is the at.% of niobium relative to silicon in the materials.…”

“…61 The materials were used in the catalytic reactions without calcination (only washing with acetone and ethanol, and drying at 65 °C; samples denoted as SiNb x -NC) or after calcination at 400 °C (air, 5 h, 1 °C min −1 ; samples denoted as SiNb x ). 61 In the sample names, x is the at.% of niobium relative to silicon in the materials.…”

“…5 nm) uniformly distributed within mesoporous silica, with Nb at.% relative to Si of 7, 20, 42, 65 and 82; the specific surface area ( S BET ) of the SiNb x was in the range 224–913 m 2 g −1 and the average mesopore sizes were in the range 7–27 nm (Table S4†). 61 SiNb x contained 138–267 μmol TAS g −1 of total amount of Lewis plus Brønsted acid sites (TAS) and a Lewis/Brønsted molar ratio (L/B) of 1.8–3.7. 61 Increasing x led to increasing L/B ratio, but the relation between x and TAS was not linear: for x = 7 (L/B = 1.8, TAS = 138 μmol g −1 ); x = 20 (L/B = 2.4, TAS = 195 μmol g −1 ); x = 42 (L/B = 2.9, TAS = 267 μmol g −1 ); x = 65 (L/B = 3.1, TAS = 252 μmol g −1 ); and x = 82 (L/B = 3.7, TAS = 156 μmol g −1 ) (Table S4†).…”

“…61 SiNb x contained 138–267 μmol TAS g −1 of total amount of Lewis plus Brønsted acid sites (TAS) and a Lewis/Brønsted molar ratio (L/B) of 1.8–3.7. 61 Increasing x led to increasing L/B ratio, but the relation between x and TAS was not linear: for x = 7 (L/B = 1.8, TAS = 138 μmol g −1 ); x = 20 (L/B = 2.4, TAS = 195 μmol g −1 ); x = 42 (L/B = 2.9, TAS = 267 μmol g −1 ); x = 65 (L/B = 3.1, TAS = 252 μmol g −1 ); and x = 82 (L/B = 3.7, TAS = 156 μmol g −1 ) (Table S4†). 61 Pure Nb 2 O 5 (1.5–5 nm particle size) synthesized in a similar fashion to SiNb x , but without silicon, possessed lower S BET (161 m 2 g −1 ) and TAS (150 μmol g −1 , L/B = 4.0) than SiNb x with x in the range 20–82.…”

“…59 Zeolites were modified with niobium in order to trigger Fur condensation, 60 and a preliminary study showed good catalytic potential of niobium oxide nanoparticles wrapped within a mesoporous silica component. 61…”