Natural Zeolites as Green Catalysts in Biomass Pyrolysis: Trends, Challenges and Perspectives from a Bibliometric Review

Abstract

Biomass pyrolysis has emerged as a key thermochemical pathway for generating renewable fuels and chemicals. However, the high oxygen content and inherent instability of bio-oil remain major challenges, hindering its commercial application. Zeolite catalysts are widely employed to improve product selectivity and enhance bio-oil stability, yet the high cost and energy-intensive synthesis of synthetic zeolites constrain their large-scale use. In this review, we provide a comprehensive analysis of natural zeolites as cost-effective and sustainable alternatives for catalytic biomass pyrolysis. A bibliometric assessment of 230 publications indexed in the Scopus database (2000-2025) was conducted to elucidate research trends, identify highly cited contributions, and highlight emerging knowledge gaps. The thematic analysis was guided by research questions focused on comparative catalytic performance, modification strategies and sustainability considerations. The results indicate that natural zeolites, such as clinoptilolite, can enhance liquid yields and improve fuel properties; however, their selectivity toward aromatics is generally lower than that of synthetic zeolites, such as HZSM-5. Modification approaches —including acid treatment, ion exchange and metal impregnation— significantly increase the acidity and porosity of natural zeolites, thereby promoting deoxygenation and hydrocarbon formation. Beyond catalytic performance, natural zeolites offer distinct sustainability benefits, including lower cost, reduced energy demand and a smaller carbon footprint. Nevertheless, challenges remain, related to structural heterogeneity, catalyst deactivation and limited pilot-scale validation. This review underscores the promising yet underexplored potential of natural zeolites for scalable, environmentally sustainable biomass valorization, while outlining key research directions to enhance catalytic efficiency and industrial applicability.