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Bio-oil is a mixture of organics produced from pyrolysis of biomass. The organics in bio-oil serve as the feedstock for the production of hydrogen, chemicals, biofuels, and carbon materials. In many processes for conversion of bio-oil, heating is required. The thermal treatment of bio-oil induces the polymerization/cracking of the organics in bio-oil, producing coke. Coke could lower the carbon conversion efficiency of bio-oil, clog the reactor chamber, and deactivate the catalyst, imposing the main challenge for the utilization of bio-oil involving the heating of bio-oil. This review investigates the coking issues in the processes for bio-oil upgrading including esterification, hydrotreatment, catalytic pyrolysis, pyrolysis, steam reforming, and the process for the conversion of bio-oil to carbon materials. The properties of coke formed from thermal treatment of bio-oil, the mechanism for coking of bio-oil, and the methods developed for tackling the coking of bio-oil are the focus.

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Selectively hydrogenating the carbonyl of furfural and opening of the furan ring is challenging but crucial for efficient conversion of furfural to pentanediols, the valuable chemicals. In this study, CuMgAl catalysts with highly dispersed Cu particles and tunable basic sites were synthesized with layered double hydroxides as precursors for hydrogenation of furfural to furfuryl alcohol (FA) and the subsequent hydrogenolysis of FA to 1,2-pentanediol and 1,5-pentanediol. The presence of varied content of Mg in the catalyst promoted dispersion of copper oxide and exposure of metallic copper species, weakened interaction between copper oxides and the carrier, suppressed sintering of metallic copper species, and increased abundance of the basic sites, promoting the catalytic activity/selectivity/stability. Strong chemical adsorption of the furan ring in FA on basic sites of the catalyst suppressed hydrogenation of the furan ring and facilitated opening of the furan ring in FA, the rate-determining step for formation of the diols.

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