Department of Chemical and Biological Engineering, University of Saskatchewan, Saskatoon, SK S7N 5A9, Canada.
Department of Engineering, Faculty of Agriculture, Dalhousie University, Truro, NS B2N 5E3, Canada.
Molecules. 2023 Jun 30;28(13):5137. doi: 10.3390/molecules28135137.
Supercritical water gasification has emerged as a promising technology to sustainably convert waste residues into clean gaseous fuels rich in combustible gases such as hydrogen and methane. The composition and yield of gases from hydrothermal gasification depend on process conditions such as temperature, pressure, reaction time, feedstock concentration, and reactor geometry. However, catalysts also play a vital role in enhancing the gasification reactions and selectively altering the composition of gas products. Catalysts can also enhance hydrothermal reforming and cracking of biomass to achieve desired gas yields at moderate temperatures, thereby reducing the energy input of the hydrothermal gasification process. However, due to the complex hydrodynamics of supercritical water, the literature is limited regarding the synthesis, application, and performance of catalysts used in hydrothermal gasification. Hence, this review provides a detailed discussion of different heterogeneous catalysts (e.g., metal oxides and transition metals), homogeneous catalysts (e.g., hydroxides and carbonates), and novel carbonaceous catalysts deployed in hydrothermal gasification. The article also summarizes the advantages, disadvantages, and performance of these catalysts in accelerating specific reactions during hydrothermal gasification of biomass, such as water-gas shift, methanation, hydrogenation, reforming, hydrolysis, cracking, bond cleavage, and depolymerization. Different reaction mechanisms involving a variety of catalysts during the hydrothermal gasification of biomass are outlined. The article also highlights recent advancements with recommendations for catalytic supercritical water gasification of biomass and its model compounds, and it evaluates process viability and feasibility for commercialization.
超临界水气化作为一种有前途的技术，可将废物残渣可持续地转化为清洁的气态燃料，其中富含氢气和甲烷等可燃气体。水热气化产生的气体组成和产率取决于工艺条件，如温度、压力、反应时间、原料浓度和反应器几何形状。然而，催化剂在增强气化反应和选择性改变气体产物组成方面也起着至关重要的作用。催化剂还可以促进生物质的水热重整和裂解，在中等温度下实现所需的气体产率，从而降低水热气化过程的能量输入。然而，由于超临界水的复杂流体动力学，关于用于水热气化的催化剂的合成、应用和性能的文献有限。因此，本综述详细讨论了用于水热气化的不同多相催化剂（例如金属氧化物和过渡金属）、均相催化剂（例如氢氧化物和碳酸盐）和新型碳质催化剂。文章还总结了这些催化剂在加速生物质水热气化过程中特定反应（如水煤气变换、甲烷化、加氢、重整、水解、裂解、键断裂和解聚）方面的优点、缺点和性能。概述了涉及各种催化剂的不同反应机制在生物质水热气化过程中。文章还强调了最近在生物质催化超临界水气化及其模型化合物方面的进展，并评估了该工艺在商业化方面的可行性和实用性。
