Fundamental Study of Catalytic Functionalities Involved in Effective C–O Cleavage over Ru-Supported Catalysts

Abstract

Catalytic hydrodeoxygenation (HDO) has been considered as a promising route for biomass revalorization. The development of active and stable materials has been undertaken over the past decade, and precious metals have displayed high activities. Ru has exhibited an outstanding performance due to its high hydrogenation capacity, among other properties. Rational development of these catalysts requires understanding the contribution of properties like acidity, oxophilicity, reducibility, and capacity to generate oxygen vacancies. However, the fundamental basis for effective C–O cleavage is not well understood, to our knowledge. Therefore, this work aimed to evaluate the effect of support in HDO of ethanol, cyclohexanol, and phenol as oxygenated model molecules for bio-oil on Ru catalysts. A series of 0.6 wt % Ru catalysts were prepared by wet impregnation with Ru­(NO)­(NO3)3 solutions. A strong influence of support in HDO activity of different molecules with the Ru catalyst was evidenced. Differences in activity on the catalyst with comparable particle size indicated that reactions involving the C–O cleavage by hydrogenation did not occur only on metallic sites. Rather, the activity took place by a cooperative action between the metallic phase and the support. For the HDO reaction of the studied molecules, Ru/TiO2 and Ru/ZrO2 were the most active solids as compared with Ru/SiO2 and Ru/Al2O3. Ethanol and cyclohexanol dehydration-reformation reactions showed that catalytic functionalities could be tuned with the reaction temperature. It was found that acid properties were more relevant when the temperature was increased (formation of ethylene and diethyl ether). At the same time, the metallic (dehydrogenation) function decreased (formation of acetaldehyde and its reformation to methane and CO). The usage of oxyphilic supports with oxygen vacancies, moderate acid site density, and redox properties in combination with high hydrogenating capacity metals like Ru may be the clue to developing highly active materials for alternative fuel production.

Hydrodeoxygenation and hydrodenitrogenation of n-hexadecanamide over Pt catalysts: effect of the support

“…These weak Lewis acid sites can be oxophilic incompletely coordinated Zr or Ce cations. 29,[85][86][87][88][89][90] Pt/CeO 2 -ZrO 2 was more active than Pt/ ZrO 2 , which, considering the H 2 -TPR, XPS, and pyridine FTIR analysis, may be due to the enhanced reducibility of the support and higher concentration of Lewis acid sites (Fig. 2, Table 3).…”

“…The HDO of C16 acid to C16 alcohol likely occurred through the adsorption of C16 acid onto the Lewis acid sites of the supports and hydrogenolysis catalyzed by Pt. 14,29,32 The HDO of C16 alcohol to the C16 paraffin may have proceeded similarly or through dehydration via an E2 mechanism involving Lewis acid-base site pairs (Table 3) followed by Pt-catalyzed hydrogenation. [81][82][83] The adsorption and dehydration of C16 alcohol may alternatively have occurred on Brønsted acid sites in the case of Pt/30SiO 2 -70Al 2 O 3 .…”

“…18 The acidity and reducibility of the catalyst support are known to affect the activity and selectivity of noble metal catalysts in the HDO of oxygen-containing compounds. 14,[29][30][31] Lewis acid sites bond to and activate carbonyl and hydroxyl groups, whereas Brønsted acid sites confer dehydration and isomerization activity. 14,[31][32][33] The enhancing effect of reducible supports on HDO activity has been attributed to the catalytic activity of oxophilic Lewis acid sites for materials such as ZrO 2 and CeO 2 -ZrO 2 , and strong metal-support interactions for materials such as Nb 2 O 5 and TiO 2 .…”

“…14,[31][32][33] The enhancing effect of reducible supports on HDO activity has been attributed to the catalytic activity of oxophilic Lewis acid sites for materials such as ZrO 2 and CeO 2 -ZrO 2 , and strong metal-support interactions for materials such as Nb 2 O 5 and TiO 2 . 29,32,[34][35][36][37] Based on HDO studies on supported noble metal catalysts and the findings of Liu et al 26 and Shimizu et al, 18 the acidity and reducibility of the catalyst support can therefore be expected to influence the activity and selectivity of noble metal catalysts in the HDN and HDO of primary amides.…”

Water-assisted single-step catalytic hydrodeoxygenation of polyethylene terephthalate into gasoline- and jet fuel-range cycloalkanes over supported Ru catalysts in a biphasic system

“…In addition, the exceptionally high activity of Ru/TiO 2 in PET hydrogenolysis may be attributed to the following aspects: (1) the oxophilic property of the TiO 2 support favors CO bond hydrogenation. 47 (2) TiO 2 is an oxide enriched with surface hydroxyl groups, which renders TiO 2 more hydrophilic. The presence of spillover H 2 and surface OH groups may further promote catalyst hydrophilicity.…”