Studies On Ni-Based Catalyst Of CH₄/CO₂ Reforming To Syngas

With the rapid development of modern industrial and socio-economic activities, the contradictions of energy consuming and supplying have become increasingly prominent. Due to the extreme use of coal and oil for a long period, their storage decreased rapidly, meanwhile the use of coal, oil and other fossil fuels has brought increasingly serious environmental problems. China’s oil reserve is not optimistic, and the use of coal has a big pressure on the environment. Fortunately, China’s natural gas and shale gas are expected to have huge reserves, probably ranking the first in the world. Therefore, with the increasing shortage of oil resources, natural gas can partially replace oil as an important chemical raw material in this century due to its cost advantage and large reserves; at the same time natural gas chemical industry also provides an important support for the sustainable development of China’s energy and environment.Synthesis gas reformed from natural gas can be further synthesized for methanol, acetic acid, synthetic diesel oil and other important chemical raw materials. Natural gas reforming methods include dry and wet reforming. Although wet reforming method is mainly employed in industry at present, the carbon dioxide reforming method（dry reforming） is not only a rational use of natural resources, but also an alleviation of the greenhouse effect. In China, natural gas and shale gas areas are often in lack of fresh water resources, in addition biomass gasification products contain large amounts of methane and carbon dioxide. Therefore dry reforming of methane is of more practical significance for China. Carbon dioxide reforming of methane to syngas has become a research direction which has received more and more attention in recent years.Previous studies showed nickel based catalyst has a high performance/price ratio in the reaction of carbon dioxide reforming of methane, hence has a broad application prospect. In our study, Ni/KIT-6 catalysts were first synthesized with different Ni loading contents via impregnation method. The results demonstrate that the 8% Ni content Ni/KIT-6 catalysts has the best catalytic activity among these catalysts; either higher or lower Ni loadings worsen the performance of the catalysts. These results indicate that KIT-6 has certain high temperature resistance property; the Ni particles dispersion affects the conversion rate of methane. We also prepared CeO₂ support using KIT-6 as a template, then prepared Ni/CeO₂ catalysts. Using Ni/CeO₂ catalysts, the reactivity of dry reforming methane was investigated. The results show that with the same nickel particle loading, at lower temperatures Ni/CeO₂ catalyst has higher methane conversion rate than Ni/KIT-6. However, high temperature is usually required to obtain a high conversion rate of methane. At high temperatures, CeO₂ is easily sintered and loses its support capability.As widely accepted, the main drawback of nickel based catalyst is its easy carbon deposition and deactivation. Since simple impregnation method and mesoporous materials as we used forpreparation of Ni/KIT-6 and Ni/CeO₂ catalysts cannot produce strong metal-support interaction, metal particles are easily sintered with poor carbon deposition resistance and finally lead to the catalyst deactivation. In order to make nickel based catalyst withbetter catalytic properties, longtime stability and excellent resistance to carbon deposition, we use a facile hydrothermal method to prepare hierarchical hollow Ni/SiO₂ nanocomposite catalyst for dry reforming catalysis of methane（DRM）. For comparison, Ni/SiO₂ is also prepared by conventional impregnation method. The hierarchical hollow Ni/SiO₂ nanocomposite has a surface area of 405.6 m2/g and significantly improved resistance to sintering and carbon deposition at high temperatures. The superior catalytic performance of the hierarchical hollow Ni/SiO₂ nanocomposite over the Ni/SiO₂ from conventional impregnation method is attributed to strong metal-support interaction between the nickel nanoparticles and the silica support. This strong interaction is resulted from the evolution of nickel nanoparticles via decomposition reduction of hierarchical phyllosilicate precursor at high temperatures in hydrogen.