An overview of catalysts in biomass pyrolysis for production of biofuels

Abstract

<em>In-situ</em> catalytic pyrolysis of biomass has been extensively studied in recent years for cost-competitive production of high quality bio-oil. To achieve that, numerous catalysts have been studied to facilitate <em>in-situ</em> upgrading of low-grade condensable vapors (bio-oil) by converting oxygenated compounds and large-molecule species. In this review, these catalysts are categorized in different families and a systematic evaluation of the catalyst effects on pyrolysis products and their characteristics is carried out with respect to the scale of the experimental setup. Among these catalysts, microporous zeolites are considered as most promising in terms of performance and the potential to tailor the desired bio-oil properties. More specifically, the prominent advantages of zeolites include efficient deoxygenation and molecular weight reduction of the resultant bio-oil, while the main drawbacks are decreases in the yield of bio-oil's organic phase and catalyst deactivation by coke deposition. In addition to the zeolite-based catalysts, other catalysts including mesoporous aluminosilicates, a widely-applied class of catalysts used for deoxygenation of bio-oil as well as alkaline compounds are also reviewed and discussed herein. The research on the latter has not been extensive but the preliminary results have revealed their potential for deoxygenation of bio-oil, production of hydrocarbons, and reduction of undesired compounds. Nevertheless, these catalysts need to be further investigated systematically. Overall, further development of dedicated catalysts for selective deoxygenation and cracking of bio-oil would be essential for scaling up the existing pyrolysis technologies to achieve commercial production of biofuels through pyrolysis.