Cu−Ni−Al Spinel Oxide as an Efficient Durable Catalyst for Methanol Steam Reforming

Improved Low-Temperature Hydrogen Production from Aqueous Methanol Based on Synergism between Cationic Pt and Interfacial Basic LaOx

Aqueous phase reforming of methanol (APRM) is simple, inexpensive and provides a high hydrogen gravimetric density of 18.8 wt. %, and so is superior to traditional gas-phase reactions performed at relatively high temperatures. In the present work, the interface between Pt nanoparticles and a TiN support was modified using a highly dispersed amorphous LaOx phase. The resulting Pt/LaOx /TiO(N) exhibited enhanced activity and long-term stability during the APRM reaction under base-free conditions compared with Pt catalysts supported on unmodified TiN or crystalline La2 O3 . The interfacial amorphous LaOx phase promoted the deposition of small Pt nanoparticles having a narrow size distribution, and also generated electron-deficient Pt. An assessment of kinetic isotope data and theoretical investigations demonstrated that the cationic Pt nanoparticles facilitated the cleavage of O-H and C-H bonds in methanol while the amorphous LaOx enhanced the dissociation of water, thus enabling the water-gas shift reaction under mild conditions.

A review study on methanol steam reforming catalysts: Evaluation of the catalytic performance, characterizations, and operational parameters

Conventional fossil-based energy sources have numerous environmental demerits; sustainable and renewable sources are attracting the undivided attention of researchers owing to their valuable physical and chemical features. Several industrial-scale technologies are employing hydrogen as a green energy source as the most preferential source. Not only is hydrogen a potent energy carrier but also it is not detrimental to the environment. Among many other hydrogen production processes, steam reforming of methanol (SRM) is deemed a practical method due to its low energy consumption. Cu, Ni, noble metals, etc., are the salient catalysts in SRM. Many researchers have conducted thorough studies incorporating improvement of the catalysts’ activity, mechanism predictions, and the impacts of operational parameters and reformers. This review concentrates on the SRM catalysts, supports, promoters, and the effect of the operational parameters on the process efficiency and H2 production yield. In this regard, the methanol conversion, H2 and CO selectivity, and operating parameters are notably contingent on the surface characterization and chemistry of the catalysts. Herein, Cu-, Ni-, and noble metal-based catalysts on various metal oxide supports, such as Al2O3 and ZnO, are assessed meticulously in the SRM process from the standpoint of mechanism and catalyst characterization. Most of the peer-reviewed studies had encountered agglomeration, metal particle sintering at high temperatures, coke formation, and deactivation of catalysts as the prevalent barriers. Hence, the novel methods of conquering the above-mentioned obstacles are evaluated in this review. Employment of diverse synthetic methods, bimetallic catalysts, distinct catalyst promoters, and unconventional supports, such as metal–organic frameworks, carbon nanotubes, and zeolites, are the salient routes to overcome the metal dispersion and thermal stability issues. In addition, the influence of operational parameters (temperature of the process, steam/carbon ratio, and feed flow rate) has been weighed painstakingly, along with introducing the research gap and future perspectives in the territory of SRM catalysts.

Advances in Enhancing the Stability of Cu-Based Catalysts for Methanol Reforming

The advent of fuel cells has led to a series of studies on hydrogen production. As an excellent hydrogen carrier, methanol can be used for reforming to produce hydrogen. Copper-based catalysts have been widely used in methanol reforming due to their high catalytic activity and low-cost preparation. However, copper-based catalysts have been subjected to poor stability due to spontaneous combustion, sintering, and deactivation. Thus, the research on the optimization of copper-based catalysts is of great significance. This review analyzes several major factors that affect the stability of copper-based catalysts, and then comments on the progress made in recent years to improve the catalytic stability through various methods, such as developing preparation methods, adding promoters, and optimizing supports. A large number of studies have shown that sintering and carbon deposition are the main reasons for the deactivation of copper-based catalysts. It was found that the catalysts prepared by the modified impregnation method exhibit higher catalytic activity and stability. For the promoters and supports, it was also found that the doping of metal oxides such as MgO and bimetallic oxides such as CeO2-ZrO2 as the support could present better catalytic performance for the methanol reforming reaction. It is of great significance to discover some new materials, such as copper-based spinel oxide, with a sustained-release catalytic mechanism for enhancing the stability of Cu-based catalysts. However, the interaction mechanism between the metal and the support is not fully understood, and the research of some new material copper-based catalysts in methanol reforming has not been fully studied. These are the problems to be solved in the future.

Effective Low-Temperature Methanol Aqueous Phase Reforming with Metal-Free Carbon Dots/C3N4 Composites

Methanol aqueous phase reforming (MAPR) reaction under mild conditions is one of the most practical ways to generate hydrogen (H₂), in which the liquid vaporization unit could be removed by the water phase reforming, making the structure of an in situ H₂ production reactor more compact. In this work, the H₂ production performances of the metal-free catalyst, N-doped carbon dots/g-C₃N₄ (NCDs/g-C₃N₄; CN-x) composites, was investigated for the MAPR reaction under low temperature and normal pressure. The optimized metal-free catalyst (NCDs/g-C₃N₄; CN-0.7) displays a H₂ yield of 19.5 μmol g^-1 h^-1 at 80 °C. More importantly, a clear understanding on the effective MAPR reaction at low temperature and normal pressure was acquired from in situ diffuse reflectance FTIR spectroscopy and the transient photovoltage test. The introduction of NCDs leads to the localization of surface charge, which is beneficial to the selective adsorption and polarization activation of polar molecules on the catalyst surface. This work provides a new strategy for the carbon-based catalyst design of the MAPR reaction at low temperatures.