A review on the role of hierarchical zeolites in the production of transportation fuels through catalytic fast pyrolysis of biomass

Abstract

Design of highly active catalysts plays a critical role in catalytic fast pyrolysis (CFP) of lignocellulosic biomass. Advanced catalysts can improve the deoxygenation rate of pyrolysis vapors and boost the production of fuel precursors. Zeolites are suitable frameworks for catalyzing pyrolysis vapors into species of transportation fuel value. However, their nano-sized structure limits the diffusion of reactants into pores and over active sites. Consequently, the aggregation of large molecules outside micropores leads to a massive coke formation, blocking pore channels, and thus, preventing the accessibility to acid sites. This could cause quick deactivation and instability of the catalyst, necessitating frequent catalyst regeneration and replenishment. Hierarchical micro/mesopore-structured zeolites are promising candidates to cope with the mentioned challenges. In addition to their adjusted pore structure and increased accessibility of acid sites, the formation of mesoporosity in zeolites provides an adequate room for the deposition of additional active phases such as metal nanoparticles, further boosting the catalytic activity. Different strategies used for preparing hierarchical zeolites can tremendously alter their attributes, and consequently affect product selectivity during CFP of biomass. Focusing on the precursors of transportation fuels (i.e., aromatic hydrocarbons and olefins), the present paper critically reviews the impacts of methods used for synthesizing hierarchical zeolite, on CFP of bio-based feedstocks. Moreover, the role of metal addition to hierarchical zeolites in biomass catalytic pyrolysis is also discussed briefly. Among the different synthesis techniques, desilication treatment using alkaline solutions is the most promising owing to its simplicity, high productivity, and scalability. In terms of product selectivity, the addition of Ga species to hierarchical zeolites can increase aromatic hydrocarbons while Ce incorporation can increase the yield of valuable oxygenates such as furan. Despite the advantages of mono-metallic hierarchical zeolites in producing cherished chemicals, future studies should scrutinize the influence of bi-metallic hierarchical zeolites in bio-based CFP processes.

Selecting Catalysts for Pyrolysis of Lignocellulosic Biomass

“…As compared to beta zeolite, the acidic form produced higher amounts of aromatic hydrocarbons due to its higher mesoporosity and acidity [53]. The combination of micro-and mesoporosity reduced the tendency to sinter and to produce large metallic nanoparticles [54]. Qian et al [55] compared the production of aromatic hydrocarbons over mesoporous ZSM-5 modified with nanocellulose to conventional and alkali-treated mesoporous ZSM-5.…”

A Comprehensive Review on Zeolite Chemistry for Catalytic Conversion of Biomass/Waste into Green Fuels

“…The study employed the molecular-based strategy to connect zeolites’ metallic-centric framework and reactiveness for various substrates to acquire a robust structure. Soltanian et al (2020) described lignocellulose biomass transformation through CFP by devising extremely active catalysts [ 140 ]. The deoxygenation rate of pyrolysis vapours or gases is facilitated by sophisticated catalysts that help escalate fuel precursors generation.…”

Bioethanol and biodiesel: Bibliometric mapping, policies and future needs

“…According to the raw materials and production methods, biofuels are classified into four different generations, namely first, second, third and fourth-generation biofuels [6]. Biofuels included in the firstgeneration (1G) utilize edible biomass (such as sugar and starch) [7] and ultimately, increased the production price of edible biomass resources.…”