Steam methanol reforming (SMR) is a promising process for producing hydrogen, a key element in hydrogen energy. The efficiency of SMR directly depends on the characteristics of the catalytic system used. This review examines the main developments in catalytic systems for SMR with an emphasis on energy and mass conversion aspects.
The most common catalysts for PRM are systems based on copper supported on various carriers (Al₂O₃, ZnO, SiO₂). Copper provides high activity in the PRM reaction, while the carrier is responsible for copper dispersion and catalyst stability. An important aspect is the optimization of the catalyst composition and structure to maximize the active copper surface area and improve the mass transfer of reagents to the active sites.
Methanol is considered a promising hydrogen storage method because it has a high hydrogen content and is in liquid phase under normal conditions. The steam methanol reforming (SMR) process converts methanol into hydrogen-containing gas under mild conditions, making it a convenient source of hydrogen directly at the point of use. The main obstacle to the widespread use of SMR technology is the development of an efficient and suitable catalyst system.
Unlike existing reviews, this paper focuses on approaches to creating catalysts for PCMs from the point of view of energy and mass transfer. It considers studies aimed at increasing the catalyst service life, its resistance to coking and sintering, achieved by modifying the composition, introducing additives and optimizing the structure.
The papers on studying the mechanism of the PCM reaction under various catalytic conditions are discussed. The papers present studies on heat and mass transfer and flow distribution in the PCM reactor using catalysts of various structures. The review analyzes in detail the methods for optimizing the catalytic system to reduce energy costs during phase-transfer catalysis, as well as to increase the efficiency and rate of methanol conversion, which can lay the foundation for the practical application of the technology.
Platinum, palladium and rhodium based catalysts also demonstrate high activity in the PRM reaction. They have higher resistance to CO poisoning than copper based catalysts, which is important when using crude methanol. However, the high cost of noble metals limits their wide application.
In addition to catalyst selection, an important aspect is optimizing the SRM process conditions. This includes controlling temperature, pressure, and steam/methanol ratio. Low temperatures are favorable for SRM reaction equilibrium but may reduce the reaction rate. Optimizing these parameters, along with the use of an effective catalyst, helps to increase methanol conversion and hydrogen selectivity, maximizing the energy yield from the process. Improving the mass transfer of methanol and water to the active catalyst sites, as well as efficient removal of reaction products (CO₂), are also critical to improving the efficiency of the system.
Author: Wei-Wei Yang, Xu Ma, Xin-Yuan Tang, Pei-Yuan Dou, Yong-Jian Yang,Ya-Ling He
Institute: Key Laboratory of Thermofluid Dynamics and Engineering, Ministry of Education, School of Power and Electrical Engineering, Xi’an Jiaotong University, P.R. China