Heterogeneous catalysis is a promising technology for the valorization of renewable biomass to sustainable advanced fuels and fine chemicals. Porosity and nanostructure are the most versatile features of heterogeneous solid catalysts, which can greatly determine the accessibility of specific active sites, reaction mechanisms, and the selectivity of desirable products. Hence, the precise tuning of porosity and nanostructure has been a potential strategy towards developing novel solid catalysts with indispensable characteristics for efficient biomass valorization. Herein, we present a timely and comprehensive review of the recent advances in catalytic biomass conversions over microporous zeolites, mesoporous silicas, and nanostructured metals/metal oxides. This review covers the catalytic processing of both edible (lipids and starch) and non-edible (lignocellulose) biomass as well as their derived compounds, along with a systematic evaluation of catalyst reusability/kinetic/mechanistic aspects in the relevant processes. The key parameters essential for tailoring particle size, morphology, porosity, acid–base, and redox properties of solid catalysts are emphasized, while discussing the ensuing catalytic effects towards the selective conversion of biomass into desirable chemicals. Special attention has been drawn to understand the role of water in liquid phase biomass conversions as well as the hydrothermal stability and the deactivation of nanoporous catalysts. We believe this comprehensive review will provide new insights towards developing state-of-the-art solid catalysts with well-defined porosity and nanoscale properties for viable biomass conversion.

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Advances in porous and nanoscale catalysts for viable biomass conversion.

The kaleidoscopic applications of zeolite catalysts (zeo-catalysts) in petrochemical processes has been considered as one of the major accomplishments in recent decades. About twenty types of zeolite have been industrially applied so far, and their versatile porous architectures have contributed their most essential features to affect the catalytic efficiency. This review depicts the evolution of pore models in zeolite catalysts accompanied by the increase in industrial and environmental demands. The indispensable roles of modulating pore models are outlined for zeo-catalysts for the enhancement of their catalytic performances in various industrial processes. The zeolites and related industrial processes discussed range from the uni-modal micropore system of zeolite Y (12-ring micropore, 12-R) in fluid catalytic cracking (FCC), zeolite ZSM-5 (10-R) in xylene isomerization and SAPO-34 (8-R) in olefin production to the multi-modal micropore system of MCM-22 (10-R and 12-R pocket) in aromatic alkylation and the hierarchical pores in FCC and catalytic cracking of C4 olefins. The rational construction of pore models, especially hierarchical features, is highlighted with a careful classification from an industrial perspective accompanied by a detailed analysis of the theoretical mechanisms.

Recent advances of pore system construction in zeolite-catalyzed chemical industry processes

Hierarchical zeolites combine the intrinsic catalytic properties of microporous zeolites and the enhanced access and transport of the additional meso- and/or macroporous system. These materials are the most desirable catalysts and sorbents for industry and become a highly evolving field of important current interests. In addition to the enhanced mass transfer leading to high activity, selectivity, and cycle time, another essential merit of the hierarchical structure in zeolite materials is that it can significantly improve the utilization effectiveness of zeolite materials resulting in the minimum energy, time, and raw materials consumption. Substantial progress has been made in the synthesis, characterization, and application of hierarchical zeolites. Herein, we provide an overview of recent achievements in the field, highlighting the significant progress in the past decade on the development of novel and remarkable strategies to create an additional pore system in zeolites. The most innovative synthesis approaches are reviewed according to the principle, versatility, effectiveness, and degree of reality while establishing a firm link between the preparation route and the resultant hierarchical pore quality in zeolites. Zeolites with different hierarchically porous structures, i.e., micro-mesoporous structure, micro-macroporous structure, and micro-meso-macroporous structure, are then analyzed in detail with concrete examples to illustrate their benefits and their fabrications. The significantly improved performances in catalytic, environmental, and biological applications resulting from enhanced mass transport properties are discussed through a series of representative cases. In the concluding part, we envision the emergence of "material-properties-by-quantitative and real rational design" based on the "generalized Murray's Law" that enables the predictable and controlled productions of bioinspired hierarchically structured zeolites. This Review is expected to attract important interests from catalysis, separation, environment, advanced materials, and chemical engineering fields as well as biomedicine for artificial organ and drug delivery systems.

Hierarchically Structured Zeolites: From Design to Application.

The highly dispersed Pd nanoparticles supported UiO-66 catalysts were successfully prepared via ethylene glycol reduction method (Pd-U-EG). And their catalytic performances were evaluated by toluene degradation. A series of characterization methods were carried out to characterize the physicochemical properties of the samples. During the effect of high weight hourly space velocity, stability and reusability test, the catalytic activity of Pd-U-EG remains unchanged, which also indicated good catalytic performance. More importantly, water resistance test (10-20 vol.% water) indicated that Pd-U-EG had a great water resistance. The study of toluene-TPD, toluene-TPSR and in-situ DRIFTS at different temperatures under different conditions over Pd-U-EG indicated the role of H2O. The introduction of H2O at low temperature was conducive to the adsorption of toluene, but inhibited the degradation of toluene. Differently, the H2O presence at high temperature was favorable to toluene degradation. In addition, toluene degradation mechanism was also revealed.

Excellent catalytic activity and water resistance of UiO-66-supported highly dispersed Pd nanoparticles for toluene catalytic oxidation

Understanding the enhancement of catalytic performance for olefin cracking: Hydrothermally stable acids in P/HZSM-5

Green and efficient epoxidation of propylene with hydrogen peroxide (HPPO process) catalyzed by hollow TS-1 zeolite: A 1.0 kt/a pilot-scale study

Post-synthesis alumination of SBA-15 in aqueous solution: A versatile tool for the preparation of acidic Al-SBA-15 supports

ZSM-5 zeolites, Ga modified via different methods (in situ hydrothermal synthesis, mechanical mixing, incipient wetness impregnation, solid-state ion exchange, and liquid phase ion exchange), were ...

Ga Substitution during Modification of ZSM-5 and Its Influences on Catalytic Aromatization Performance

Hierarchical TS-1 with intracrystalline voids could be synthesized by post-modification with tetrapropyl ammonium hydroxide (TPAOH), however the process was supposed to be restrained by the charge balance effect. In order to release the constraint, NH3·H2O was introduced in the post-modification. The influences of the TPAOH/NH3·H2O modification, the TPAOH concentration and the modification time on the physiochemical properties were studied. The dissolution process and recrystallization process were observed in the combined modification, and both of them were intensified by the NH3·H2O introduced, indicating that the constraint on the OH− diffusion was released. Owing to the intensified processes, the TPAOH concentration and post-modification time could be reduced, and hierarchical TS-1 with relative high crystallinity, less defect sites and a larger secondary pore volume (about 0.18 cm3 g−1) was achieved in 4 h. However, the combined-modification exerted little influence on the chemical composition and acidity, and the microporous properties were almost the same with that of TS-1 modified with TPAOH only. The secondary porosity in the combined-modified samples were mainly intracrystalline voids, and grooves on the surface were also found. Although extra-framework titanium species were created by the post-modification, part of the titanium was still in the framework position. The catalytic activity was evaluated by phenol hydroxylation and 1-octene epoxidation, and better catalytic activity was achieved for the improved accessibility of the active sites.

Xingtian Shu

Papers

Green and efficient epoxidation of propylene with hydrogen peroxide (HPPO process) catalyzed by hollow TS-1 zeolite: A 1.0 kt/a pilot-scale study

Post-synthesis alumination of SBA-15 in aqueous solution: A versatile tool for the preparation of acidic Al-SBA-15 supports

Ga Substitution during Modification of ZSM-5 and Its Influences on Catalytic Aromatization Performance

Hierarchical TS-1 synthesized effectively by post-modification with TPAOH and ammonium hydroxide

The synthesis, characterization and catalytic activity of the hierarchical TS-1 with the intracrystalline voids and grooves