Alternative Monomers Based on Lignocellulose and Their Use for Polymer Production.

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.

Biomass has been long exploited as an anthropogenic energy source; however, the 21st century challenges of energy security and climate change are driving resurgence in its utilization both as a renewable alternative to fossil fuels and as a sustainable carbon feedstock for chemicals production. Deconstruction of cellulose and hemicellulose carbohydrate polymers into their constituent C5 and C6 sugars, and subsequent heterogeneously catalyzed transformations, offer the promise of unlocking diverse oxygenates such as furfural, 5-hydroxymethylfurfural, xylitol, sorbitol, mannitol, and gluconic acid as biorefinery platform chemicals. Here, we review recent advances in the design and development of catalysts and processes for C5–C6 sugar reforming into chemical intermediates and products, and highlight the challenges of aqueous phase operation and catalyst evaluation, in addition to process considerations such as solvent and reactor selection.

Heterogeneously Catalyzed Hydrothermal Processing of C5–C6 Sugars

The utilization of CO2 as a carbon source for synthesis of value-added chemicals and fuels, particularly light olefins, is one of the most attractive routes to convert CO2 as part of a large-scale process. Designing active, selective, and stable catalysts for olefin production is challenging because of the difficulty characterizing structure–property relationships for the highly complex CO2 hydrogenation reaction network. To understand the challenges and opportunities in converting CO2 directly to olefins over a single tandem catalyst, this Perspective reviews the following three routes: (1) direct hydrogenation of CO2 to olefins over promoted catalysts; (2) methanol synthesis followed by methanol-to-olefins (MeOH-mediated route); (3) CO production via the reverse-water–gas-shift reaction, followed by Fischer–Tropsch synthesis (CO-mediated route). Future research directions are proposed on the critical research areas of elucidating reaction mechanisms by combining in situ characterization techniques with ...

Development of Tandem Catalysts for CO2 Hydrogenation to Olefins

Catalytic conversion of cellulose to ethylene glycol (EG) or 1,2-propylene glycol (1,2-PG) represents an attractive approach in the valorization of biomass, due to the high atom economy of the reaction process and large market demand of the diol products. The one-pot catalytic conversion of cellulose is a complex reaction network, comprising hydrolysis, retro-aldol condensation, hydrogenation, isomerization, dehydrogenation, thermal side reactions, etc. In addition to EG and 1,2-PG, a variety of byproducts such as sorbitol, mannitol, erythritol, 1,2-butanediol, and glycerol may be coproduced. The key point for obtaining high selectivity for EG or 1,2-PG lies in effective control of the major reaction steps in the reaction network proceeding at matching rates. In this Perspective, we depict the general reaction route for glycol production from cellulose and summarize the active elements for the retro-aldol condensation reaction, which is the determinant step for the formation of C2 and C3 intermediates. In...

Selectivity Control for Cellulose to Diols: Dancing on Eggs

The influence of different iron carbides on the activity and selectivity of iron-based Fischer–Tropsch catalysts has been studied. Different iron carbide phases are obtained by the pretreatment of a binary Fe/SiO2 model catalyst (prepared by coprecipitation method) to different gas atmospheres (syngas, CO, or H2). The phase structures, compositions, and particle sizes of the catalysts are characterized systematically by XRD, XAFS, MES, and TEM. It is found that in the syngas-treated catalyst only χ-Fe5C2 carbide is formed. In the CO-treated catalyst, Fe7C3 and χ-Fe5C2 with a bimodal particle size distribution are formed, while the H2-treated catalyst exhibits the bimodal size distributed e-Fe2C and χ-Fe5C2 after a Fischer–Tropsch synthesis (FTS) reaction. The intrinsic FTS activity is calculated and assigned to each corresponding iron carbide based on the phase composition and the particle size. It is identified that Fe7C3 has the highest intrinsic activity (TOF = 4.59 × 10–2 s–1) among the three candidat...

Relationship between Iron Carbide Phases (ε-Fe2C, Fe7C3, and χ-Fe5C2) and Catalytic Performances of Fe/SiO2 Fischer–Tropsch Catalysts

A series of Pd–WOx/Al2O3 catalysts with different contents of WOx were prepared by stepwise incipient wetness impregnations. The influence of WOx on the physicochemical properties of Pd–WOx/Al2O3 catalysts, as well as their catalytic performance for the hydrogenolysis of glucose to 1,2-propanediol (1,2-PDO), was investigated. At low surface W density (0.3–2.1 W nm–2), distorted isolated WOx and oligomeric WOx are present on the Pd–WOx/Al2O3 catalysts. Furthermore, isolated WO4 are the dominating species on the Pd–WOx(5%)/Al2O3 catalyst. When the W density increased to 3.1 W nm–2, polymeric WOx species are dominant on the Pd–WOx(30%)/Al2O3 catalyst. The Pd surface area decreased while the acid amount increased with increasing W density. Furthermore, increased Lewis acid sites are provided by isolated WO4 and oligomeric WOx species whereas increased Bronsted acid sites exist on polymeric WOx species. Lewis acid sites promote glucose isomerization to fructose, which is an intermediate in glucose hydrogenolys...

Effect of WOx on Bifunctional Pd–WOx/Al2O3 Catalysts for the Selective Hydrogenolysis of Glucose to 1,2-Propanediol

WOx modified Cu/Al2O3 as a high-performance catalyst for the hydrogenolysis of glucose to 1,2-propanediol

Glucose is the most abundant platform molecule of biomass in nature. High value-added chemicals and liquid fuels can be obtained by selectively breaking C–C/C–O bonds and removing surplus oxygen in glucose. This article focuses on glucose hydrogenolysis over a wide variety of transition metal catalysts (Cu/C, Ni/C, Pt/C, Pd/C, Ru/C, Rh/C, Ir/C). Liquid and gas phase after reaction mainly contain three types of products such as polyols, alkanes, furans. Many value-added chemicals and liquid fuels were obtained, such as sorbitol, 1,2-propanediol, ethylene glycol, 2,5-dimethylfuran, 2,5-dimethyltetrahydrofuran, hexane, etc. Different metal catalysts showed different selectivities to these products. Typically, at hydrogenation conditions of 453 K and 4.0 MPa, glucose was largely converted to C1 products over the Ru/C catalyst. Pd/C selectively converted glucose into C2 and C3 products. C6 products were most selective over Pt/C. The hydrogenation/hydrogenolysis capabilities of different metals for C–C and C–O bonds, the endocyclic C C and C–O–C bonds are also quite different. For example, Pt/C provides the weakest hydrogenolysis activity to C–O and C–C bonds. Ru/C possesses the highest activity to C–C and C–O bond cleavage. Meanwhile, it is most active for C–O–C bond hydrogenation in glucose at low temperature. Cu/C exhibits the weakest endocyclic C C bond hydrogenation activity in furan ring. The reaction pathway of glucose hydrogenolysis over different metal catalysts was also outlined.

Chengwei Liu

Papers

Relationship between Iron Carbide Phases (ε-Fe2C, Fe7C3, and χ-Fe5C2) and Catalytic Performances of Fe/SiO2 Fischer–Tropsch Catalysts

Effect of WOx on Bifunctional Pd–WOx/Al2O3 Catalysts for the Selective Hydrogenolysis of Glucose to 1,2-Propanediol

WOx modified Cu/Al2O3 as a high-performance catalyst for the hydrogenolysis of glucose to 1,2-propanediol

Aqueous-phase hydrogenolysis of glucose to value-added chemicals and biofuels: A comparative study of active metals

Facile Large-Scale Synthesis of Nanoscale Fayalite, α-Fe2SiO4