Abstract
In this work, the introduction of modifying additives in the composition of catalysts is considered as an effective mode of improving functional characteristics of materials for two processes of methane conversion into valuable products – methane dehydroaromatization (DHA of CH4) into benzene and hydrogen and autothermal reforming of methane (ATR of CH4) into synthesis gas. The effect of type and content of promoters on the structural and electronic state of the active component as well as catalyst activity and stability against deactivation is discussed. For DHA of CH4 the operation mode of additives M = Ag, Ni, Fe in the composition of Mo-M/ZSM-5 catalysts was elucidated and correlated with the product yield and coke content. It was shown that when Ag serves as a promoter, the duration of the catalyst stable operation is enhanced due to a decrease in the rate of the coke formation. In the case of Ni and Fe additives, the Ni-Мо and Fe-Mo alloys are formed that retain the catalytic activity for a long time in spite of the carbon accumulation. For ATR of CH4, the influence of M = Pd, Pt, Re, Mo, Sn in the composition of Ni-M catalysts supported on La2O3 or Ce0.5Zr0.5O2/Al2O3 was elucidated. It was demonstrated that for Ni-M/La2O3 catalysts, Pd is a more efficient promoter that improves the reducibility of Ni cations and increases the content of active Nio centers. In the case of Ni-M/Ce0.5Zr0.5O2/Al2O3 samples, Re is considered the best promoter due to the formation of an alloy with anti-coking and anti-sintering properties. The use of catalysts with optimal promoter type and its content provides high efficiency of methane valorization processes.
Highlights
Catalytic processes play a crucial role in our lives
The introduction of modifying additives into the composition of Ni catalyst is a rather wide-spread approach directed to the improvement of functional characteristics of catalysts developed for various catalytic processes (Fig. 11) [114,115,116,117,118,119,120,121,122,123,124,125,126,127,128,129,130,131,132,133,134,135,136,137,138,139]
With the aim of development of an efficient catalyst for methane conversion into hydrogencontaining gas, we studied the effect of the Pd content and the synthesis method (Ni+Pd combined impregnation, Pd/Ni sequential impregnation, Ni/Pd sequential impregnation) on physicochemical and catalytic properties of NiPd/CeZrO2/Al2O3 [147]
Summary
Catalytic processes play a crucial role in our lives. Biocatalysts ‒ enzymes ‒ control all biochemical processes in nature and, in essence, underlie life on Earth [1, 2]. The specifics of the strategy will depend on the chemical composition and physicochemical properties of the catalyst and the mechanism of its deactivation in real conditions of the catalytic process It is known [55,56,57,58,59,60,61,62,63,64] that the introduction of modifying additives into the catalyst composition allows the control of the dispersion and redox properties of the active component and correspondingly the improvement of the activity and stability of catalytic systems. For the development of methods for direct regulation of catalyst physicochemical properties and activity it is interesting to carry out a comparative study of the effects of different additives on the catalyst physicochemical properties and functional characteristics in methane conversion to value-added chemical products and semi-products. On the basis of comparing results of characterization of catalysts by a complex of instrumental methods (low-temperature nitrogen adsorption, X-ray diffraction, transmission electron microscopy, temperature-programmed reduction by hydrogen) and their catalytic activity, the interrelation “composition-structure-properties” has been established, and the optimal additives (both type and content) for each process have been found
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