Hydrodeoxygenation of Lignin-Derived Compound Mixtures on Pd-Supported on Various Oxides

Abstract

As a plethora of different unsaturated oxygenates is produced from the pyrolysis of biomass into bio-oil, understanding the role of competitive adsorption in catalytic upgrading is essential. To this end, the relative reactivities of representative molecules of key families within a single feed mixture were examined through reaction testing and in situ infrared spectroscopy characterization. The influence of the support (silica, ceria, zirconia, titania, and niobia) on the rate of elimination of hydroxyl and methoxy groups was evaluated on single compounds (phenol, m-cresol, and anisole) and binary mixtures (phenol/ anisole and m-cresol/anisole). The removal of hydroxyl groups depends significantly on the support type. Pd supported on SiO 2 and CeO 2 favored ring hydrogenation resulting in the production of oxygenated products such as cyclohexanone/3methylacylohexanone. The use of ZrO 2 , TiO 2 , and Nb 2 O 5 as supports promotes the formation of benzene/toluene by hydrogenation of the carbonyl group of the tautomer intermediate formed or even direct deoxygenation. The reaction pathways for removal of methoxy groups also depend on the support. The demethylation route that yields methane and phenol and its further deoxygenation to benzene is proposed to take place over all catalysts, except on Pd/Nb 2 O 5 . Due to the superior oxophilicity of Nb cations, the niobia-supported catalyst greatly favors the direct deoxygenation, with formation of benzene and methanol (demethoxylation). The reaction with binary mixtures of phenol/anisole and m-cresol/anisole revealed that the hydroxyl groups react preferentially. Insight into the mode and strength of adsorption of the different molecules on the catalyst surface was obtained by DRIFTS analysis upon adsorption and desorption. The results indicate that under the HDO reaction conditions investigated phenol and m-cresol seem to adsorb more strongly on the catalyst surface and react more readily than anisole. Thus, this study shows that competitive adsorption is a predominant factor impacting product selectivity.

Toward Value-Added Arenes from Lignin-Derived Phenolic Compounds via Catalytic Hydrodeoxygenation

“…Arenes, such as benzene, toluene, and xylene (BTX), are a versatile class of raw materials for chemical production and are widely used in the fuel, rubber, fiber resin, pharmaceutical, textile, fragrance, and paper industries. − At present, the preparation of arenes is generally dependent on nonrenewable fossil resources (Figure a). − The excessive reliance on fossil feedstocks has led to the problems of an energy crisis and environmental deterioration, which promotes the development of green and sustainable energy sources. − Particularly, the production of arenes from renewable biomass has the advantages of low pollution and greenhouse gas emission, while the petroleum refining process produces large amounts of byproducts and other toxic gases and wastes, which seriously pollute the environment. Biomass, as a cheap and abundant renewable resource in nature, can be translated into various value-added functional chemicals and fuels. − Accordingly, under the global theme of advocating both carbon neutrality and low carbon economy, the utilization of biomass resources to produce high-valued arenes has attracted great interest and attention from researchers worldwide (Figure b). − …”

Rare‐Earth Metal Yttrium‐Modified Composite Metal Oxide Catalysts for High Selectivity Synthesis of Biomass‐Derived Lactic Acid from Cellulose

“…Therefore, it could speculate that different metal oxide supports had a significant influence on the catalytic performance of yttrium-modified composite metal oxide catalysts, and the main reason may be the discrepancy in physical properties of catalysts, such as BET surface areas, pore volume as well as the intrinsic property in individual oxide. [22] In addition, combined with the characterization results of NH 3 -TPD, PyIR, and experimental results, it can observe that introduction of yttrium species markedly resulted in the change of the surface weak acidity and Lewis acidity of catalysts, which could promote the occurrence of retro-aldol condensation reaction to form lactic acid, and efficiently inhibited the dehydration reaction of fructose to HMF. Although the amount of weak acidity of Y 2 O 3 /Al 2 O 3 was smallest among them, whereas gave a higher yield of lactic acid than other catalysts screened, testifying that appropriated weak acidity were favorable for the formation of lactic acid.…”

“…Particularly, Y 2 O 3 /Al 2 O 3 exhibited prominent reactivity for the conversion of cellulose with 72.8 % yield of lactic acid, which was much higher than those of Y 2 O 3 /ZrO 2 and Y 2 O 3 /ZnO, and the lactic acid yield of 62.5 % and 43.8 % could be obtained, respectively. Therefore, it could speculate that different metal oxide supports had a significant influence on the catalytic performance of yttrium‐modified composite metal oxide catalysts, and the main reason may be the discrepancy in physical properties of catalysts, such as BET surface areas, pore volume as well as the intrinsic property in individual oxide [22] . In addition, combined with the characterization results of NH 3 ‐TPD, PyIR, and experimental results, it can observe that introduction of yttrium species markedly resulted in the change of the surface weak acidity and Lewis acidity of catalysts, which could promote the occurrence of retro‐aldol condensation reaction to form lactic acid, and efficiently inhibited the dehydration reaction of fructose to HMF.…”

Experimental and ab initio Investigation on the Effect of CO and CO2 during Hydrodeoxygenation of m‐Cresol over Co/SBA‐15

“… the direct deoxygenation (DDO route) leading to toluene, either by the direct cleavage of the C−O bond or by involving the formation of a tautomer intermediate (3‐methyl‐3,5‐cyclohexadienol) with further hydrogenation of its carbonyl group; the hydrogenation (HYD route) in which the aromatic ring is first hydrogenated yielding 3‐methylcyclohexanone and 3‐methylcyclohexanol with further dehydration to produce methylcyclohexenes and final hydrogenation to methylcyclohexane. Direct cleavage of 3‐methylcyclohexanol to methylcyclohexane can also be considered [6d,16] . The hydrogenation route also involves the passage through the tautomer intermediate (3‐methyl‐3,5‐cyclohexadienol) which can be considered as a common intermediate of both DDO and HYD routes. …”