Activation strategies for biochar to use as an efficient catalyst in various applications

•Biochar obtained from thermochemical methods can be activated by various strategies.•Physical viz., steam and CO2 based activation of biochar is used.•Activation of biochar by H2O2, KOH, ZnCl2, K2CO3 are chemical methods.•Activated biochar has improved surface area, pore size and minimal contaminants.•Activated biochar is used as catalyst for biodiesel production. Microalgae and macroalgae are known for their use in food and fuel applications. Recently, tremendous interest on algal biomass for biochar production has been increased. Biochar are well known for its catalytic activity to produce many finished products such as alternative fuels, treat environmental waste water and act as an input for agricultural applications. Three routes are commonly adopted for alternative fuel production from algal biomass namely, biochemical, chemical, and thermochemical techniques. Recently, thermochemical methods for the conversion of algal biomass to biochar are employed to use biochar based catalyst. Biochar must be activated before used as a potential catalyst. Therefore, this review has given broad information of various activation strategies for biochar modification. Different activation methods such as physical and chemical modes are being practiced to modify the biochar for efficient catalyst in alternative fuel production.