A critical review of the use of nanomaterials in the biomass pyrolysis process

The bio-oil produced from the biomass pyrolysis process requires complex and expensive upgrading before being used in existing energy/chemical systems. The catalytic pyrolysis process can substantially reduce the complexity and cost of bio-oil upgrading while providing an opportunity to engineer product distribution. The bulk heterogeneous catalysts usually applied in catalytic pyrolysis suffer from uneven or inactivated catalytic sites, lowering their activity and reusability performance. Nanotechnology can effectively resolve the drawbacks of conventional catalysts while improving the quality and quantity of bio-oil. Hence, this article thoroughly reviews and critically discusses the use of nanomaterials in biomass pyrolysis. A systematic literature review is conducted to find the most relevant published articles on applying nanocatalysts in biomass pyrolysis. The effects of catalysts on biomass pyrolysis and their various types and application modes (i.e., in-situ and ex-situ) are explained. Biomass decomposition pathways and product distribution patterns in nanocatalyst-assisted pyrolysis are explained. The literature data on using of nanocatalysts in biomass pyrolysis is collected and analyzed. Overall, bio-oil production by nanocatalysts is over 35% greater than that of bulk catalysts. Compared to bulk catalysts, nanocatalysts produce bio-oil with over 10%, 20%, 60%, and 15% more phenol, alcohol, aldehydes, and ketones. Nanocatalysts double furan production over bulk catalysts. Nevertheless, hydrocarbon production and acid formation are more than double with bulk catalysts rather than nanocatalysts. Bulk catalysts produce 10% more ester than nanocatalysts. In addition, over 20% more bio-oil is produced by in-situ nanocatalytic pyrolysis than by ex-situ pyrolysis. The pros and cons of using nanocatalysts in the biomass pyrolysis process are discussed, and future research directions are suggested to fill the existing gaps. Overall, much progress needs to be made to use nanocatalysts in industrial-scale pyrolysis processes.