High Efficient Hydrogenation of Lignin-Derived Monophenols to Cyclohexanols over Pd/γ-Al2O3 under Mild Conditions

Abstract

Abstract:The catalytic hydrogenation of lignin-derived monophenols with high efficiency and selectivity is important for the sustainable production of chemicals and fuels. Here, Pd/γ-Al 2 O 3 was prepared via impregnation and used as catalyst for the hydrogenation of phenols to cyclohexanols under mild conditions in aqueous solution. 3 wt. % Pd/γ-Al 2 O 3 exhibited good catalytic activity for the selective hydrogenation of 4-ethylphenol into 4-ethylcyclohexanol, and a conversion of 100% with selectivity of 98.9% was achieved at 60˝C for 12 h. Other lignin-derived monophenolic model compounds such as 4-methyl phenol and 4-propyl phenol could be hydrogenated into cyclohexanols selectively under optimal conditions. Moreover, the Pd/γ-Al 2 O 3 catalyst displayed good activity for the hydrogenation of the mixture of monophenols directly derived from raw biomass system to cyclohexanols as the main products, and was favorable for the depolymerization of lignin oligomers under milder conditions. Pd/γ-Al 2 O 3 catalyst showed good water resistance and stability after recycling four times. This result might provide a promising approach to selectively producing cyclohexanol directly from raw biomass material under mild conditions in aqueous solutions.

Two-step hydrogen transfer catalysis conversion of lignin to valuable small molecular compounds

“…Typically, the dry raw material is rapidly heated to a high temperature (over 450°C) under anerobic environment and the condensation of the pyrolysis steam results in liquid product. Lignin is generally thermally depolymerized to phenols, aromatic hydrocarbons, or aliphatic hydrocarbons during pyrolysis [8,9]. Catalytic pyrolysis is the other method used to deoxygenate pyrolysis biomass [10].…”

Production of Biofuel via Hydrogenation of Lignin from Biomass

“…Pd also exhibits a good metal to be doped with Al 2 O 3 as a catalyst for hydrogenation process using wet impregnation technique. The work of Yi et al (2016) [54] employed 3 wt.%Pd/ Al 2 O 3 to convert 4-ethylphenol to cyclohexanols under mild reaction conditions in an aqueous phase. The reaction exhibits 100% conversion at 60°C for 12 h TOS.…”

Biotransformation of lignin: Mechanisms, applications and future work

“…Thermochemical processes mainly include pyrolysis, [21][22][23] gasification, [24][25][26] oxidation, 27,28 hydrogenation, [29][30][31][32] etc. Thermochemical processes mainly include pyrolysis, [21][22][23] gasification, [24][25][26] oxidation, 27,28 hydrogenation, [29][30][31][32] etc.…”

“…Currently, there are two major platforms for lignin conversion: thermochemical and biological approaches. Thermochemical processes mainly include pyrolysis, [21][22][23] gasification, [24][25][26] oxidation, 27,28 hydrogenation, [29][30][31][32] etc. These processes typically break down large molecules of lignin by applying harsh conditions, such as high temperature, high pressure, and extreme pH 33 while catalysts are usually used.…”