A review on biochar production techniques and biochar based catalyst for biofuel production from algae

•Biochar and hydrochar was produced from pyrolysis and HTC, respectively.•Biochar composition and its significance over other catalyst was highlighted.•Underlying mechanism of biochar catalyst facilitated fuel production was given.•Biochar catalyst was used in transesterification, biohydrogen, biomass hydrolysis. Thermochemical routes namely pyrolysis, hydrothermal carbonization, torrefaction and hydrothermal liquefaction yields biochar product, which mainly contains carbon, oxygen and hydrogen. Biochar produced can be activated to employ as a potential catalyst in various energy production applications like transesterification and fermentation. In this regard, this article has comprehensively reviewed the biochar based catalyst for fuel production. Initially, biochar produced from various thermochemical routes and its yield was presented. Composition of biochar produced from sundry feedstock was reviewed and the reason for choosing biochar catalyst for fuel production was discussed. Eventually, mechanism by which the biochar catalyst facilitates the fuel production was given for better understanding. Transesterification and esterification reaction for biodiesel, biomass hydrolysis process and biohydrogen production facilitated by biochar catalyst were extensively discussed.