Tuning combined steam and dry reforming of methane for "metgas" production : A thermodynamic approach and state-of-the-art catalysts

Abstract

Nowadays, combined steam and dry reforming of methane (CSDRM) is viewed as a new alternative for the production of high-quality syngas (termed as "metgas", H2:CO of 2.0) suitable for subsequent synthesis of methanol, considered as a promising renewable energy vector to substitute fossil fuel resources. Adequate operation conditions (molar feed composition, temperature and pressure) are required for the sole production of "metgas" while achieving high CH4, CO2 and H2O conversion levels. In this work, thermodynamic equilibrium analysis of CSDRM has been performed using Gibbs free energy minimization where; (i) the effect of temperature (range: 200–1000 °C), (ii) feed composition (stoichiometric ratio as compared to a feed under excess steam or excess carbon dioxide), (iii) pressure (range: 1–20 bar) and, (iv) the presence of a gaseous diluent on coke yields, reactivity levels and selectivity towards "metgas" were investigated. Running CSDRM at a temperature of at least 800 °C, a pressure of 1 bar and under a feed composition where CO2+H2O/CH4 is around 1.0, are optimum conditions for the theoretical production of "metgas" while minimizing C(s) formation for longer experimental catalytic runs. A second part of this work presents a review of the recent progresses in the design of (principally) Ni-based catalysts along with some mechanistic and kinetic modeling aspects for the targeted CSDRM reaction. As compared to noble metals, their high availability, low cost and good intrinsic activity levels are main reasons for increasing research dedications in understanding deactivation potentials and providing amelioration strategies for further development. Deactivation causes and main orientations towards designing deactivation-resistant supported Ni nanoparticles are clearly addressed and analyzed. Reported procedures based on salient catalytic features (i.e., acidity/basicity character, redox properties, oxygen mobility, metal-support interaction) and recently employed innovative tactics (such as confinement within mesoporous systems, stabilization through core shell structures or on carbide surfaces) are highlighted and their impact on Ni0 reactivity and stability are discussed. The final aspect of this review encloses the major directions and trends for improving synthesis/preparation designs of Ni-based catalysts for the sake of upgrading their usage into industrially oriented combined reforming operations.