Study On The Catalytic Performance Of Ni-based Catalyst Supported On Dealuminated Beta Zeolite For Propane Dehydrogenatio

Direct dehydrogenation of propane to propylene is one of the core reaction processes for industrial propylene production,and the current industrial catalysts for this reaction system are Pt-based and Cr-based catalysts of noble metals.In order to reduce the cost of catalyst and further improve the catalytic performance,further development of high-performance,economical and environmentally friendly Ni-based catalysts with transition metal Ni as the main active component has become a hot research topic in this field.However,due to the extremely strong activation ability of Ni species for C-H and C-C bonds,which can easily lead to the deep oxidation of the product propylene,how to effectively regulate the valence state of Ni metal and the ratio between it and other additives is the key that Ni-based catalysts can be effectively used for propane dehydrogenation reaction.In this work,dealuminized Beta zeolite with large specific surface area,unique pore structure and a large number of T vacancies was selected as the carrier,and loaded Ni-based catalysts with some different active species were prepared by conventional impregnation method,and direct dehydrogenation of propane to propylene was used as the model reaction,and the effects of the dispersion state of Ni species on the carrier surface,valence state and its interaction with the carrier on the activity,selectivity and stability of Ni-based catalysts were systematically studied.selectivity and stability of the Ni-based catalysts,and higher activity and stability of the propane dehydrogenation reaction were obtained at low Ni loading through the anchoring effect of the dealuminated Beta zeolite T vacancies;based on the successful preparation of the mono-Ni catalysts,alkaline earth metal Ca and rare earth metal Ce were introduced as additives to the Ni-based catalysts,and the performance of the catalysts was further improved through the regulation of the active component formulation to optimize the active component ratios of the loaded nickel-based catalysts were optimized.For the representative catalyst samples,the correlation between the physical structure of the catalyst and its catalytic performance was investigated by using the characterization techniques such as X-ray diffraction（XRD）,programmed temperature rise reduction（H₂-TPR）,X-ray photoelectron spectroscopy（XPS）and propane programmed temperature rise desorption（C₃H₈-TPD）,respectively,during the reaction process,the influence of the adsorption and desorption between the product and the active component of the catalyst on the reaction activity and selectivity was investigated by some in situ characterization tools such as C₃H₈-DRIFTS and C₃H₆-DRIFTS.The main findings obtained from this work are as follows.（1）The results of the study on the dealuminated Beta zeolite loaded Ni catalyst showed that when the loading of Ni was 0.5 wt%,it exhibited excellent catalytic performance for the direct dehydrogenation of propane,and the initial conversion of propane could reach 42.7%at600℃,and the selectivity of propylene was stabilized at 87%after 2 h of reaction;the low loading of Ni was highly dispersed on the carrier surface,and the vacant sites formed by the dealuminated Beta zeolite anchor the Ni species so that Ni enters the framework structure of zeolite and forms the structure of Si-O-Ni,which can generate more L-acid sites and improve the stability of Ni species,making Ni an effective active site for the propane dehydrogenation reaction,thus improving the reaction activity and propylene selectivity.（2）Based on the successful preparation of a loaded mono-Ni catalyst sample 0.5Ni%wt-Beta with good catalytic performance for propane dehydrogenation,different contents of alkaline earth metal Ca were introduced to modify the active component Ni,respectively,and the results of catalyst physical characterization showed that the introduction of Ca further improved the dispersion of Ni,made it easier to enter the zeolite pore channel,In addition,improved the interaction of Ni with the carrier through the internal Si-OH.The introduction of Ca modulates the electronic environment of Ni on the surface to some extent and changes the interaction between the active component and the carrier,thus improving the reactivity of Ni species;the catalytic reaction results show that at 600℃,the sample of Ni:Ca atomic molar ratio of 1:1 catalyst at 600℃ reached an initial conversion of propane of 76.7%,and after 2 h of reaction,the selectivity of propylene could be increased to 94.7%.（3）Similarly,the introduction of different contents of rare earth metal Ce to modify the loaded mono-Ni catalyst sample 0.5wt%Ni-Beta,the results of catalyst physical characterization showed that the entry of Ni into the lattice of Ce O₂ improved its dispersion,reduced the formation of Ni O,increased the concentration of L acid on the catalyst,and changed the electronic environment of Ni due to the existence of electron transfer between Ni and Ce,that can improve its reactivity;the model reaction characterization results showed that the activity of propane dehydrogenation reaction on the Ni-based catalyst modified by Ce was significantly improved,and the initial conversion of propane reached 64.5%for the catalyst sample with the Ni:Ce atomic molar ratio of 1:1 at 600℃,and the selectivity of propylene could be increased to 89.3%after 2 h of reaction.