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

Catalytic partial oxidation of methane has been reviewed with an emphasis on the reaction mechanisms over transition metal catalysts. The thermodynamics and aspects related to heat and mass transport is also evaluated, and an extensive table on research contributions to methane partial oxidation over transition metal catalysts in the literature is provided. Presented are both theoretical and experimental evidence pointing to inherent differences in the reaction mechanism over transition metals. These differences are related to methane dissociation, binding site preferences, the stability of OH surface species, surface residence times of active species and contributions from lattice oxygen atoms and support species. Methane dissociation requires a reduced metal surface, but at elevated temperatures oxides of active species may be reduced by direct interaction with methane or from the reaction with H, H2, C or CO. The comparison of elementary reaction steps on Pt and Rh illustrates that a key factor to produce hydrogen as a primary product is a high activation energy barrier to the formation of OH. Another essential property for the formation of H2 and CO as primary products is a low surface coverage of intermediates, such that the probability of O–H, OH–H and CO–O interactions are reduced. The local concentrations of reactants and products change rapidly through the catalyst bed. This influences the reaction mechanisms, but the product composition is typically close to equilibrated at the bed exit temperature.

A review of catalytic partial oxidation of methane to synthesis gas with emphasis on reaction mechanisms over transition metal catalysts

A review of the main developments in the partial oxidation of methane to synthesis gas since the first paper in 1929 to the present day is given. The reaction is discussed from the view of the thermodynamics; the main catalysts studied for the reaction are summarised, and the reaction mechanism is discussed. The review is not comprehensive, but it is designed to provide a general background to the most important developments in the field.

Brief Overview of the Partial Oxidation of Methane to Synthesis Gas

The production of high-demand chemical commodities such as ethylene and propylene (methanol-to-olefins), hydrocarbons (methanol-to-hydrocarbons), gasoline (methanol-to-gasoline) and aromatics (methanol-to-aromatics) from methanol—obtainable from alternative feedstocks, such as carbon dioxide, biomass, waste or natural gas through the intermediate formation of synthesis gas—has been central to research in both academia and industry. Although discovered in the late 1970s, this catalytic technology has only been industrially implemented over the past decade, with a number of large commercial plants already operating in Asia. However, as is the case for other technologies, industrial maturity is not synonymous with full understanding. For this reason, research is still intense and a number of important discoveries have been reported over the last few years. In this review, we summarize the most recent advances in mechanistic understanding—including direct C–C bond formation during the induction period and the promotional effect of zeolite topology and acidity on the alkene cycle—and correlate these insights to practical aspects in terms of catalyst design and engineering. The conversion of methanol — which can be produced from non-fossil resources — to important chemical commodities such as olefins and aromatics allows for the diversification of organic feedstocks beyond petrochemicals. This Review covers recent discoveries about the mechanism of this process and discusses how these link to practical aspects in reaction engineering.

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Recent trends and fundamental insights in the methanol-to-hydrocarbons process

The effect of Ni content on the Ni/Ce-ZrO2 catalyst has been investigated in the methane conversion reactions to syngas, such as oxy-reforming, steam reforming and oxy-steam reforming. Among the catalysts examined, Ni/Ce-ZrO2 catalyst with 15% Ni loading exhibits not only the highest catalytic activity and selectivity but also remarkable stability. The TPR results reveal that strong interaction between support and metal exists and that some part of NiO incorporates into the surface of the Ce-ZrO2 support. Combined with H2 chemisorption results, one may deduce that Ni surface area and the chemical environment of nickel, as well as the properties of the Ce-ZrO2 support, play very important roles in the catalytic activity and stability of Ni/Ce-ZrO2 catalysts. It seems that two kinds of active sites, i.e. one for methane and the other for steam or oxygen, are well-balanced on 15% Ni/Ce-ZrO2 catalyst.

Methane reforming over Ni/Ce-ZrO2 catalysts: effect of nickel content

Systematic studies have been conducted over several selected H-zeolites, namely HZSM-5, H-Beta, HY, nano HZSM-5, HZSM-11 and nano HZSM-11, aimed to investigate influence of the channel structure on catalytic performance for gas phase dehydration of glycerol to acrolein. Compared to H-Beta and HY, improved catalytic performance was discovered over HZSM-5, which demonstrated that H-zeolites with smaller channels, the ones marginally larger than the molecular diameter of glycerol, were preferential for the reaction. HZSM-11, with lower channel complexity, was more likely to obtain superior catalytic performance due to enhanced diffusion. Nano HZSM-11 (300–500 nm) exhibited excellent catalytic performance with 81.6 mol% glycerol conversion and 74.9 mol% acrolein selectivity at GHSV as high as 873 h −1 (TOS = 8 h). BET and TEM experiment results indicated that coke was initially deposited at channel intersections of H-zeolites, and when the channel blockage came up to a certain extent, there arrived the onset of coke deposition on the external surface.

Study on the influence of channel structure properties in the dehydration of glycerol to acrolein over H-zeolite catalysts

The two-stage riser catalytic cracking for maximizing propylene yield has the following characteristics:  relative lower temperature with larger catalyst/oil ratio, stratified injections of various feedstocks, and proper contacting time between catalyst and oil vapor. These characteristics can enhance catalytic cracking and minimize thermal cracking, which is very favorable for maximizing propylene yield and lowering dry gas. The experimental results showed that using the special catalyst LTC-2 the yield of propylene is up to 24.11% and the liquid yield approaches 82% when the first stage riser is fed Daqing AR with butenes and the second is fed the light gasoline and heavy oil from the first stage. The final gasoline containing only 26% olefins and nearly 50% aromatics is the desired high octane-number component. The diesel must be hydrogenated due to its higher density.

Maximizing propylene yield by two-stage riser catalytic cracking of heavy oil

Effects of ammonium exchange and Si/Al ratio on the conversion of methanol to propylene over a novel and large partical size ZSM-5

In-situ synthesis and catalytic activity of ZSM-5 zeolite

A comprehensive investigation into the effect of seed on the crystallization of ZSM-5 in the absence of template was performed by introducing seeds with different frameworks and pore structures into the gel mixture. It was found that the crystallization behavior of template-free ZSM-5 was strongly governed by three key factors in a synergetic way. Firstly, the common composite building units contained in the seed and product zeolites crucially promoted the nucleation and subsequent crystal growth of target zeolites. Secondly, the terminal TOH units on the surface of seed crystals strengthened their recognition capacity to the composite units formed in systems, which significantly accelerated the crystallization process. Thirdly, the external surface area provided by seeds offered specific sites for composite building units to attach to and pile up to form new zeolitic layer. Thus, in this work, ZSM-5 or ZSM-11 zeolites with terminal TOH were viewed as the preferable seeds to induce the formation of ZSM-5 in a short period (12–16 h) without template addition and the crystal size could be easily controlled just by using seeds with different external surface area.

Chunyi Li

Papers

Study on the influence of channel structure properties in the dehydration of glycerol to acrolein over H-zeolite catalysts

Maximizing propylene yield by two-stage riser catalytic cracking of heavy oil

Effects of ammonium exchange and Si/Al ratio on the conversion of methanol to propylene over a novel and large partical size ZSM-5

In-situ synthesis and catalytic activity of ZSM-5 zeolite

Inductive effect of various seeds on the organic template-free synthesis of zeolite ZSM-5