Catalytic hydropyrolysis of biomass using natural zeolite-based catalysts

Natural clinoptilolite (coded as Escott), synthetic BEA, and mixed Escott-BEA zeolites supported nickel and iron catalysts were employed for catalytic hydropyrolysis of eucalyptus globulus leaves. Comparing non-catalytic pyrolysis and catalytic pyrolysis in N2, the use of catalysts along with H2 (30 bar) resulted in improved yields of liquid oil and gas products, with reduced production of biochar/coke. Moreover, the biochar from catalytic hydropyrolysis showed a higher mesopore surface area (97 m2/g) than non-catalytic biochar (74 m2/g). Incorporating a small amount of BEA into Escott weakens the metal-support interaction, enhances H2 adsorption activity and increases the catalyst acidity, leading to an improved aromatic monomers selectivity while preventing excessive cracking of liquid oil. Consequently, Ni-Fe/Escott-BEA catalyst shows the highest content of valuable liquid organic components. Ni-Fe/Escott, with the largest Ni particles and lowest acidity, exhibits higher selectivity to methane and naphthalenes products. In contrast, Ni-Fe/BEA with excessive acid sites exhibited significantly lower content of liquid organic products but higher yields of C2-C5 gas products and deposited carbon, primarily ascribed to its high acidity promoting coupling, cracking and deoxygenation reactions. The deactivation of Bronsted acid sites was more pronounced than Lewis acid sites, underscoring their crucial role in coupling reactions and leading to increased coke deposition.