ArticlLight olefins are high value-added chemical products of fossil fuels, which are widely used in production of fine chemicals, plastics, coatings, cosmetics, etc. However, the traditional method for producing light olefins is steam cracking of naphtha under high temperature and pressure, which apparently exhibits many problems, such as high energy input, low efficiency, energy resources waste, etc.

In order to solve these problems, researchers apply a series of transition metal catalysts to directly or indirectly turn syngas (CO+H₂) into light olefins, such process is call Fischer-Tropsch (F-T) reaction. Through years of study, such widely used transition metal catalysts are iron and cobalt-based catalysts. In such catalysts, active metals are loaded on different supports, like alumina, molecular sieve, then tuned or modified by promoter (Na, K, Mn, etc.) to gain higher reaction activity or selectivity. However, due to extremely strong hydrogenation ability and low C-C couple ability, nickel catalysts tend to produce methane or other low carbon saturated hydrocarbons in F-T reaction. Therefore, it is of great significance to utilize active nickel-based catalysts to be more preferred in producing light olefins by weaken the hydrogenation ability. A group from Center of Supramolecular Photochemistry, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, made thorough investigation into such subject. The relative results were published on Advanced Energy Materials, December 16, 2019.

The group synthesized a novel manganese oxide modified metallic nickel catalyst (Ni/MnO), the hydrogenation ability of active metal Ni were obviously decreased which were caused by tuning of electronic structure by MnO and finally led to significant increase in light olefins selectivity. Precursor materials were simply synthesized through double drop method, and a series Ni/MnO catalysts with various degrees of reduction were gained via controlling reduction temperatures. Through UV-visible light irradiating on such catalysts, compared to catalysts which metallic nickel were directly supported by alumina, selectivity of light olefins was increased several times. In addition, photo-thermal contrast experiments and flow system reactions proved that the process is photothermal driven reaction with fine catalytic stability. X-ray photoelectron spectroscopy, X-ray absorption fine structure carried out at BSRF and density functional theory calculation further explained that such performance is caused by electron enrichment due to transformation of electron from MnO to active metal Ni, thus decreasing hydrogenation energy barrier and desorption barrier of unsaturated reaction intermediate, and eventually leading to tremendously increasing light olefins selectivity.

This study provides a possibility for the application of nickel-based catalysts with strong hydrogenation ability in F-T synthesis industry as well as ideas for the research of tuning catalytic hydrogenation ability. Synchrotron sources help solve the key problem of structure-performance relationship in this study.

Article:

Yuanshen Wang, Yufei Zhao, Jinjia Liu, Zhenhua Li, Geoffrey I. N. Waterhouse, Run Shi, Xiaodong Wen and Tierui Zhang* Manganese Oxide Modified Nickel Catalysts for Photothermal CO Hydrogenation to Light Olefins, Adv. Energy Mater., 2019, 1902860.