Hydrogen production reactions from carbon feedstocks: fossil fuels and biomass.

3.2. Preparation 4090 3.3. Intermediate Layers 4090 3.4. Support 4090 3.5. Modification 4091 3.5.1. Silica Membrane Modification 4091 3.5.2. Membrane Structure Modification 4092 3.6. Operational Stability 4092 4. Zeolite Membranes 4092 4.1. Membrane Growth Methods 4093 4.2. Permeation and Gas Transport 4093 4.3. Defect Site Diffusion/Nonzeolitic Pores 4094 4.4. Thin Films 4094 4.5. Zeolite Membrane Modification 4094 4.6. CO2 Sequestration in H2 Separations 4095 4.7. Manufacturing 4095 5. Carbon-Based Membranes 4096 5.1. Carbon Membrane Preparations 4097 5.2. Carbon Membrane Post-treatment 4097 5.3. Carbon Membrane Module Construction 4097 5.4. Selective Surface Flow Membranes 4097 5.5. Disadvantages of Carbon Membranes 4098 5.6. Molecular Sieving Carbon Membranes 4098 5.7. Carbon Nanotubes 4099 6. Polymer Membranes for H2 Separations 4100 6.1. Dense Polymeric Membranes 4100 6.2. Hydrogen Selective Polymeric Membranes 4101 6.3. H2 versus CO2 Selective Polymeric Membranes 4103

Membranes for hydrogen separation.

and Perspectives Sophie Carenco,†,‡,§,∥,⊥ David Portehault,*,†,‡,§ Ced́ric Boissier̀e,†,‡,§ Nicolas Meźailles, and Cleḿent Sanchez*,†,‡,§ †Chimie de la Matier̀e Condenseé de Paris, UPMC Univ Paris 06, UMR 7574, Colleg̀e de France, 11 Place Marcelin Berthelot, 75231 Paris Cedex 05, France ‡Chimie de la Matier̀e Condenseé de Paris, CNRS, UMR 77574, Colleg̀e de France, 11 Place Marcellin Berthelot, 75231 Paris Cedex 05, France Chimie de la Matier̀e Condenseé de Paris, Colleg̀e de France, 11 Place Marcellin Berthelot, 75231 Paris Cedex 05, France Laboratory Heteroelements and Coordination, Chemistry Department, Ecole Polytechnique, CNRS-UMR 7653, Palaiseau, France

Nanoscaled metal borides and phosphides: recent developments and perspectives

The quest for an efficient process to convert methane efficiently to fuels and high value-added chemicals such as olefins and aromatics is motivated by their increasing demands and recently discovered large reserves and resources of methane. Direct conversion to these chemicals can be realized either oxidatively via oxidative coupling of methane (OCM) or nonoxidatively via methane dehydroaromatization (MDA), which have been under intensive investigation for decades. While industrial applications are still limited by their low yield (selectivity) and stability issues, innovations in new catalysts and concepts are needed. The newly emerging strategy using iron single sites to catalyze methane conversion to olefins, aromatics, and hydrogen (MTOAH) attracted much attention when it was reported. Because the challenge lies in controlled dehydrogenation of the highly stable CH4 and selective C–C coupling, we focus mainly on the fundamentals of C–H activation and analyze the reaction pathways toward selective rou...

Direct Conversion of Methane to Value-Added Chemicals over Heterogeneous Catalysts: Challenges and Prospects

The article discusses oxidation catalysis by substitutional cation doping of binary oxides. Substitutional cation doping is not the only possibility. One can imagine that replacing some anions with other anions may also be beneficial. There is evidence that the presence of small amounts of halogen in the feed or on the oxide surface improves its catalytic activity. It is very likely that doped oxide catalysts have been used before the concept was formulated explicitly. Most oxide catalysts have low levels of impurities that may be substitutional dopants. If they segregate at the surface, they can affect the catalytic activity without our knowledge even though their net concentration is very low. It is also possible that the 'as-prepared' catalyst is a doped oxide that, under reducing reaction conditions, is converted to very small metallic dopant clusters supported on the host oxide. The physical and chemical properties of such clusters are different from those of a bulk metal, and it is difficult to distinguish them from a doped oxide.

Catalysis by doped oxides.

The use of 9% La2NiO4/γ-Al2O3 (9NLA) as a catalyst for CO2 reforming of methane to syngas has been investigated in a fixed-bed reactor. The results revealed that the yields of CO and H2 over a 800 °C calcined 9NLA catalyst were remarkably higher than those over a 500 °C calcined one. The BET data confirmed that the properties, such as specific surface area, pore volume and average pore diameter, of a used and a regenerated catalyst were similar to those of a fresh catalyst. Temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS) results indicated that the activity of the catalyst depended largely on the degree of catalyst reduction, as well as on the dispersion of metallic nickel. The results of X-ray diffraction (XRD) and temperature-programmed oxidation (TPO)-MS studies demonstrated that the formation of carbon species on the catalyst could be related to the structure and surface composition of the catalyst. With the rise in temperature for catalyst calcination, there was a decline in coke formation due to the formation of a stable NiAl2O4 spinel structure.

Carbon deposition and catalyst stability over La2NiO4/γ-Al2O3 during CO2 reforming of methane to syngas

A La2NiO4/ZSM-5 catalyst was prepared by the sol–gel method, which ensured high dispersion of the metal and high activity in the CO2 reforming of methane. The catalytic performance, catalyst stability and coke deposition as well as the influence of the doped La species on the Ni/ZSM-5 catalyst were investigated. The results show that the conversion of CO2 and CH4 to syngas and the selectivity of CO and H2 observed over the La2NiO4/ZSM-5 catalyst were significantly higher than those over a Ni/ZSM-5 or La2NiO4/γ-Al2O3 catalyst. Such results suggest that the doping of the rare earth ion (La3+) in the ZSM-5 not only enhanced the stability of the catalyst, but also increased the catalytic activity. In addition, the catalysts were characterized by X-ray diffraction (XRD), BET and thermogravimetic and differential thermal analysis (TG/DTA). The X-ray diffraction (XRD) studies revealed that the prepared catalyst, La2NiO4, exhibited a typical spinel structure and was uniformly dispersed both on the surface and in the ZSM-5 zeolite channels. During the CO2/CH4 reforming, the La2O3 generated from the La2NiO4 decomposition was transformed into La2O2CO3 in an atmosphere of CO2, which promoted CO2 adsorption on the surface of the catalyst. The TG/DTA results indicate that the amount of carbon deposition on the La2NiO4/ZSM-5 catalyst was smaller than the amount on the Ni/ZSM-5 catalyst, and that there were at least two kinds of carbon deposition on the used La2NiO4/ZSM-5 catalyst. However, only one kind of carbon deposition existed on the used Ni/ZSM-5 catalyst.

Preparation of La2NiO4/ZSM-5 catalyst and catalytic performance in CO2/CH4 reforming to syngas

LaMeOx/SBA-15 (Me = Zn, Co and Fe) desulfurizers were synthesized by a sol–gel method and their performance for H2S removal from hot coal gas was investigated. The results of eight successive desulfidation–regeneration cycles revealed that the LaFeO3/SBA-15 desulfurizer shows high performance and stability for H2S removal. The results of BET, XPS, HRTEM and XRD characterization suggested that the SBA-15 structure of used LaMeOx/SBA-15 remained intact. It was found that there is only partial reduction of Fe3+ ions in LaFeO3/SBA-15 by hydrogen in hot coal gas, a factor considered to be favorable for LaFeO3/SBA-15 sulfidation. The metal oxides supported on SBA-15 can effectively suppress mechanical disintegration and improve stability of LaMeOx/SBA-15. Among the three desulfurizers, LaFeO3/SBA-15 performs the best.

Preparation and desulfurization performance of LaMeOx/SBA-15 for hot coal gas

XPS, XAES, and TG/DTA characterization of deposited carbon in methane dehydroaromatization over Ga–Mo/ZSM-5 catalyst

The catalytic performance of Zn-based/HZSM-5 catalysts prepared by wet impregnation method was investigated for the methane dehydroaromatization (MDA) reaction under the conditions of atmospheric pressure and supersonic jet expansion (SJE). The physical properties of the catalysts were characterized by Brunauer–Emmett–Teller (BET), Fourier transform infrared (FT-IR), temperature-programmed reduction of H2 (H2-TPR), temperature-programmed desorption of NH3 (NH3-TPD), X-ray photoelectron spectroscopy (XPS), thermogravimetric and differential thermogravimetric (TG/DTG), and high-resolution transmission electron microscopy (HRTEM) techniques. The results revealed that under SJE condition the Zn/HZSM-5 catalyst exhibited high catalytic activity. It was found that because of the rapid migration of H+ ions on the catalyst, the activation of CH4 at active sites of nano-ZnO is facile. A new reaction mechanism that involves an active “ZnO–CH3+...–HZnO” intermediate formed as a result of synergetic action between Zn...

Characteristic and Mechanism of Methane Dehydroaromatization over Zn-Based/HZSM-5 Catalysts under Conditions of Atmospheric Pressure and Supersonic Jet Expansion

Bingsi Liu

Papers

Carbon deposition and catalyst stability over La2NiO4/γ-Al2O3 during CO2 reforming of methane to syngas

Preparation of La2NiO4/ZSM-5 catalyst and catalytic performance in CO2/CH4 reforming to syngas

Preparation and desulfurization performance of LaMeOx/SBA-15 for hot coal gas

XPS, XAES, and TG/DTA characterization of deposited carbon in methane dehydroaromatization over Ga–Mo/ZSM-5 catalyst

Characteristic and Mechanism of Methane Dehydroaromatization over Zn-Based/HZSM-5 Catalysts under Conditions of Atmospheric Pressure and Supersonic Jet Expansion