Conversion of agricultural waste into stable biocrude using spinel oxide catalysts

A Critical Review of the Synthesis and Applications of Spinel-Derived Catalysts to Bio-Oil Upgrading

The transformation of renewable bio-oil into value-added chemicals and bio-oil through catalytic processes embodies an efficient approach within the realm of advancing sustainable energy. Spinel-based catalysts have garnered significant attention owing to their ability to precisely tune metals within the framework, thereby facilitating adjustments to structural, physical, and electronic properties, coupled with their remarkable thermal stability. This review aims to provide a comprehensive overview of recent advancements in spinel-based catalysts tailored specifically for upgrading bio-oil. Its objective is to shed light on their potential to address the limitations of conventional catalysts, thereby advancing sustainable biofuel production. Initially, a comprehensive analysis is conducted on different metal oxide composites in terms of their similarity and dissimilarity on properties. Subsequently, the synthesis methodologies of spinels are scrutinised and potential avenues for their modification are explored. Following this, an in-depth discussion ensues regarding the utilisation of spinels as catalysts or catalyst precursors for catalytic cracking, ketonisation, catalytic hydrodeoxygenation, steam and aqueous-phase reforming, as well as electrocatalytic upgrading of bio-oil, with a specific emphasis on elucidating their catalytic reactivity, and underlying structure-activity correlation and catalysis mechanisms. Finally, the challenges and potential prospects in utilising spinels for the catalytic valorisation of renewable biofuel are addressed, with a specific focus on the use of machine learning - based approaches to optimise the structure and activity of spinel catalysts. This review aims to provide specific directions for further exploration and maximisation of the spinel catalysts in the bio-oil upgrading field.

Multifunctional catalyst-assisted sustainable reformation of lignocellulosic biomass into environmentally friendly biofuel and value-added chemicals

Rapid urbanization is increasing the world's energy demand, making it necessary to develop alternative energy sources. These growing energy needs can be met by the efficient energy conversion of biomass, which can be done by various means. The use of effective catalysts to transform different types of biomasses will be a paradigm change on the road to the worldwide goal of economic sustainability and environmental protection. The development of alternative energy from biomass is not easy, due to the uneven and complex components present in lignocellulose; accordingly, the majority of biomass is currently processed as waste. The problems may be overcome by the design of multifunctional catalysts, offering adequate control over product selectivity and substrate activation. Hence, this review describes recent developments involving various catalysts such as metallic oxides, supported metal or composite metal oxides, char-based and carbon-based substances, metal carbides and zeolites, with reference to the catalytic conversion of biomass including cellulose, hemicellulose, biomass tar, lignin and their derivative compounds into useful products, including bio-oil, gases, hydrocarbons, and fuels. The main aim is to provide an overview of the latest work on the use of catalysts for successful conversion of biomass. The review ends with conclusions and suggestions for future research, which will assist researchers in utilizing these catalysts for the safe conversion of biomass into valuable chemicals and other products.

Catalytic performance of Ni-Co/HZSM-5 catalysts for aromatic compound promotion in simulated bio-oil upgrading

Bio-oil can be used as a substitute for fossil fuels after it is upgraded. Bimetal-modified HZSM-5 catalysts with various Ni-to-Co ratios were prepared to address catalysis problems, including deactivation of the catalysts and low hydrocarbon yields. The catalytic performance of Ni-Co/HZSM-5 in upgrading the simulated bio-oil was investigated with a fixed-bed reactor, and the influence of the loaded duplex metal ratio was also discussed. The new moderately strong/strong acid sites of Ni-Co/HZSM-5 changed according to the Ni/Co loading ratios, which substantially affected the acidity, catalytic activity and selectivity of the Ni-Co/HZSM-5. However, incorporating Co and Ni into the zeolite did not alter the structure of the HZSM-5. The interactions of the loaded bimetallic oxides reached equilibrium in 6Ni-4Co/HZSM-5, in which moderately strong acid sites and strong acid sites were formed after loading with Co₃O₄ and NiO. With a suitable acid site ratio, 6Ni-4Co/HZSM-5 exhibited excellent performance, with a lower coke deposition of 3.29 wt% and stable catalytic activity, and the conversion remained at 83-73% during 360 min of uninterrupted catalysis. Periodic changes in the acid sites and interfacial protons were the critical factors that improved the properties of the 6Ni-4Co/HZSM-5 and enhanced its selectivity for aromatic compounds.