Designing main-group catalysts for low-temperature methane combustion by ozone

Roles of different Ni-Si interactions in methane combustion under oscillating temperature conditions

The silicon- modified nickel oxide catalysts with the same compositions but distinct Ni-Si interactions were obtained via different synthesis routes and utilized for methane combustion under conditions of oscillating temperatures. For catalysts prepared by co-grinding, amorphous SiO2 was dispersed on the surface of large NiO crystallites. During high-temperature calcination or reactions, the crystallization of SiO2, coupled with the sintering or decomposition of NiO crystallites, led to the inferior catalytic activity and stability. Interactions between Ni and Si species were enhanced in catalysts synthesized by precipitation. The Si species was incorporated into the NiO lattice to inhibit the growth of NiO crystallites and to generate nickel silicate species under thermal treatments. The small NiO crystallites provided more Ni3+ and active oxygen species for methane activation and oxidation, while the bulk nickel silicate species played a pivotal role in improving thermal stability, conjointly provoking excellent catalytic performance in cyclic heating-cooling tests between 180 and 800 °C. This study offers new insights into the design of metal oxide composites for catalytic applications.

Low-Temperature Methane Combustion Using Ozone over Coβ Catalyst

Catalytic methane (CH4) combustion is a promising approach to reducing the release of unburned methane in exhaust gas. Here, we report Co-exchanged β zeolite (Coβ) as an efficient catalyst for CH4 combustion using O3. A series of ion-exchanged β zeolites (Co, Ni, Mn, Fe, and Pd) are subjected to the catalytic test, and Coβ exhibits a superior performance in a low-temperature region (<100 °C). The results of X-ray absorption spectroscopy (XAS) and catalytic tests for Coβ with different Co loadings indicate the isolated Co species is the plausible active site. The reaction mechanism of CH4 combustion over the isolated Co2+ cation is theoretically investigated by the single-component artificial force-induced reaction (SC-AFIR) method to thoroughly search for possible reaction routes. The resulting path toward CO2 formation shows an activation energy of 73 kJ/mol for the rate-determining step and an exothermicity of 1025 kJ/mol, which supports the experimental results. During a long-term catalytic test for 160 h without external heating, the CH4 conversion gradually decreases from 80 to 40%, but the conversion fully recovers after dehydration at 500 °C (0.5 h). The copresence of H2O and CO exhibits a negative impact on the catalytic activity, while NO and SO2 do not markedly change the catalytic activity.

Photodriven Methane Conversion on Transition Metal Oxide Catalyst: Recent Progress and Prospects

Methane as the main component in natural gas is a promising chemical raw material for synthesizing value-added chemicals, but its harsh chemical conversion process often causes severe energy and environment concerns. Photocatalysis provides an attractive path to active and convert methane into various products under mild conditions with clean and sustainable solar energy, although many challenges remain at present. In this review, recent advances in photocatalytic methane conversion are systematically summarized. As the basis of methane conversion, the activation of methane is first elucidated from the structural basis and activation path of methane molecules. The study is committed to categorizing and elucidating the research progress and the laws of the intricate methane conversion reactions according to the target products, including photocatalytic methane partial oxidation, reforming, coupling, combustion, and functionalization. Advanced photocatalytic reactor designs are also designed to enrich the options and reliability of photocatalytic methane conversion performance evaluation. The challenges and prospects of photocatalytic methane conversion are also discussed, which in turn offers guidelines for methane-conversion-related photocatalyst exploration, reaction mechanism investigation, and advanced photoreactor design.

Materials Enabling Methane and Toluene Gas Treatment

This paper summarizes the latest research results on materials for the treatment of methane, an important greenhouse gas, and toluene, a volatile organic compound gas, as well as the utilization of these resources over the past two years. These materials include adsorption materials, catalytic oxidation materials, hydrogen-reforming catalytic materials and non-oxidative coupling catalytic materials for methane, and adsorption materials, catalytic oxidation materials, chemical cycle reforming catalytic materials, and degradation catalytic materials for toluene. This paper provides a comprehensive review of these research results from a general point of view and provides an outlook on the treatment of these two gases and materials for resource utilization.