Supported MoO_x and WO_x Solid Acids for Biomass Valorization: Interplay of Coordination Chemistry, Acidity, and Catalysis

Abstract

Supported molybdenum oxide (MoO x ) and tungsten oxide (WO x ) materials are a vital class of solid acid catalysts for the chemical industry because of their nontoxic nature, strong acidity, remarkable stability in water, hydrogen, and oxygen atmospheres, and excellent reusability performance. These fascinating solid acids play a pivotal role in developing sustainable catalytic routes for renewable biomass processing to produce value-added fuels, chemicals, and platform molecules. The coordination chemistry of MoO x and WO x on the support materials (oxides, carbons, or zeolites) controls their acidic strength, active site accessibility, and catalytic activity. Hence, significant efforts have been made toward optimizing the conditions used for catalyst synthesis and biomass processing to tune the coordination chemistry of MoO x and WO x with the substrate molecules and, thus, their acid-activity/selectivity performance. This Review provides a comprehensive overview of supported MoO x and WO x solid acids for biomass valorization. The importance of the biomass and the role of solid acids for biomass valorization were emphasized, followed by a brief discussion of supported MoO x and WO x solid acids. Afterward, the interplay of coordination chemistry, acidic strength, and catalytic activity of supported MoO x and WO x solid acids was discussed. Finally, their catalytic applications for the valorization of several biomass substrates and their derivatives were summarized. This Review will provide valuable insights for developing advanced supported WO x and MoO x solid acids for catalytic biomass valorization and other challenging acid-catalyzed processes.

Multifunctional WO3–ZrO2-Supported Platinum Catalyst for Remarkably Efficient Hydrogenolysis of Esters to Alkanes

“…When the catalyst support was WO 3 dispersed on other metal oxides such as Al 2 O 3 or CeO 2 , the conversion and yield were considerably lower than those when WO 3 –ZrO 2 was used as the support (Figure , entries 6 and 7). As previously reported, WO 3 supported on ZrO 2 becomes superacidic . In our work, the superacidic nature of WO 3 –ZrO 2 can efficiently activate carbon–oxygen bonds in esters, which is responsible for the high activity of Pt(0.25)/WO 3 –ZrO 2 .…”

“…Our catalyst development was focused on the following two critical points: (i) efficient activation of carbon–oxygen bonds in ester and (ii) supplying sufficient active hydrogen species even under low hydrogen pressure. We envisioned that WO 3 nanoclusters can efficiently activate the carbon–oxygen bonds because tungsten oxide supported on certain metal oxides like ZrO 2 becomes superacidic . More importantly, WO 3 nanoclusters can function as a “hydrogen reservoir” to store hydrogen as protons and electrons owing to their redox property, which would enable the low-pressure hydrogenolysis.…”

Efficient one-pot tandem catalysis of glucose into 1,1,2-trimethoxyethane over W-Beta catalysts

“…30 The band at 1540.2 cm −1 was related to the pyridine ions formed by the interaction with the Brønsted acid sites, whose density was not more than 0.021 mmol g −1 when the tungsten content was below 4.0 wt% while the obvious increment (from 0.021 to 0.034 mmol g −1 ) was associated with the hydroxyl species of the extra-framework tungsten oxide species when the tungsten loading was 8.0 wt%. 36 The Sn-Beta catalysts exhibit a higher Lewis acid density than that of the W-Beta catalysts with the same heteroatom content (Fig. 4B) and the drop in the Lewis acid density was due to the formation of bulk SnO 2 at a high Sn loading.…”

“…Bulk WO 3 shows little ammonia adsorption at around 250 °C, which aroused from the minor W 5+ species. 36 For the desorption profiles of various zeolite catalysts, there are three distinct desorption peaks: the broad low-temperature desorption peak (at around 150 °C) corresponds to the weak Brønsted acid formed by the silanol groups, which acted as the active site for etherification. 19 However, these Brønsted acid sites were rather weak in breaking the glycosidic bonds of cellulose (Table S5†).…”

Basicity of isostructural porous ionic crystals composed of Nb/Ta-substituted Keggin-type polyoxotungstates

“…[5][6][7] A particular focus has been given on solid base catalysts, such as alkali ion-exchanged zeolites and alkaline earth metal oxides, due to their thermal stability and recyclability. [8][9][10] However, the development of solid base catalysts is well behind solid acid catalysts, [11][12][13][14] because it is difficult to construct electrically and structurally controlled uniform basic sites in solids. Therefore, the design and synthesis of solid base catalysts with well-defined active sites remain a strongly desired and challenging research subject.…”