Preparation Of Supported Co-based Silicalite-1 Catalyst And Its Performance In Propane Dehydrogenation

Propylene is an important petrochemical raw material that can be used to produce polypropylene,acrylonitrile,acrylic acid and other chemicals.Propylene mainly comes from catalytic cracking of naphtha and steam cracking process in petroleum refining.At present,the traditional propylene production process is faced with the problems of low production capacity and poor selectivity.Propane dehydrogenation process is one of the most important alternative processes for the direct propylene production.In recent years,it has been widely concerned by researchers.In this process the preparation of catalysts with high activity,high selectivity and high stability is the key issue.Among the propane dehydrogenation catalysts,the most common industrial catalysts are Pt-based and Cr O_x-based catalysts.Considering economic benefits and environmental protection,there is still a need to find alternative,environmentally friendly and inexpensive non-noble metal-based catalysts.Among which,Co-based catalysts have been gradually studied due to the higher dehydrogenation activity and selectivity.In this paper,a series of Co-based propane dehydrogenation catalysts with different loadings are prepared by using Co as the active component and Silicalite-1 with a ZSM-5 molecular sieve（MFI）framework structure as the carrier.It is used in the dehydrogenation of propane.The results showed that Co-based Silicalite-1 catalyst with5%Co loading prepared by hydrothermal method at p H of 9 exhibited excellent catalytic performance in propane dehydrogenation,and its initial propane conversion and propylene selectivity could reach 25.1%and 87.2%,respectively.Compared with the sample prepared by conventional impregnation method,the propane conversion nearly increased 15 percentage.Combined with the above reaction performance of the catalyst,the prepared catalyst was further characterized and analyzed using transmission electron microscopy（TEM）,X-ray photoelectron spectroscopy（XPS）and Raman and the Co active sites were further studied.The results showed that Co species prepared by hydrothermal method can uniformly disperse on the surface of Silicalite-1 in the form of tetra-coordinated Co²⁺.With enhancing the Co-O-Si interaction,the stability of the Co species could be improved,thus improving its catalytic performance in propane dehydrogenation.In addition,after 10 h stability test,the Co particles on the spent catalyst prepared by hydrothermal method were significantly smaller than those on the spent catalyst by impregnation method,and the carbon deposit content was also significantly lower.In order to further optimize the propane dehydrogenation performance,a series of Co-based Silicalite-1 catalysts were prepared by adjusting the preparation parameters,such as hydrothermal synthesis temperatures and preparation p H values.Applying the prepared catalyst in propane dehydrogenation,the effect of preparation parameters on the activity and stability of Co-based Silicalite-1 catalyst was investigated.Co/S-80HT prepared at hydrothermal temperature of 80℃and p H of 9 exhibited the best propane dehydrogenation performance.With the propane initial conversion and propylene initial selectivity of 28.9%and 88.1%,respectively.FT-IR and Raman characterizations further confirmed that the variation of preparation conditions could modify the formed Co active species,and modulating the propane dehydrogenation performance.This study could expend important research concept for improving the performance of non-noble Co-based catalysts in propane dehydrogenation and provide basic data for further industrial applications.