Synthesis Of Uniform Pore Structure Fe/SiO₂ Catalyst And Its Catalytic Performance In Co Hydrogenation To Lower Olefins

Lower olefins?such as ethylene,propylene,and butane?as key chemical raw materials,are usually produced by naphtha cracking or alkane dehydrogenation during the petrochemical process.With decreasing the shortage of crude oil and increasing environmental pollution,the development of processes,which are applied to obtain lower olefins by CO hydrogenation catalytic conversion from non-petroleum resources,is of strategic importance for the rational and efficient use of resources.And these processes will be very usefull for China,whose energy structure characteristics is rich coal,lean oil,and less gas.In essence,the catalytic conversion of syngas to lower olefins is a reaction of the carbon-carbon chain propagation under CO hydrogen conditions.The product distribution follows the Anderson-Schulz-Flory law,which has wide product distribution,low target product selectivity and so on.However,how to regulate the selectivity of products is still a challenge in CO catalytic hydrogenation.Therefore,studying the influence law of product selectivity is of significance for regulating product selectivity in CO hydrogenation.In order to study the influence law of product selectivity in CO hydrogenation process,monodisperse SiO₂ microspheres were orderly assembled to prepare the SiO₂material with uniform pores,and further obtained four uniform pore structure Fe/SiO₂catalyst?with different pore sizes 10⁴5 nm?after loading Fe.Afterward,the effects of reaction temperature,space velocity,the pore size,and the Fe loading on products selectivities were investigated over the as-prepared uniform pore structure Fe/SiO₂catalysts.Results show that with increasing reaction temperature,the CO conversion rate increases gradually.And the selectivities of CH₄,C⁼_2-4,and CO₂ increase slightly,while the selectivity of C₅₊decreases.However,with increasing space velocity,the CO conversion rate decreases,but the selectivity of CH₄,C⁼_2-4,and CO₂ has no change.Moreover,under the condition of 300 ^oC,1.0 MPa,with the increase of catalyst pore size,the CO conversion rate increases slightly,the selectivity of C₅₊decreases first and then increases,while the selectivity of CH₄,C⁼_2-4,and CO₂ increases first and then decreases.With the increasing loading of Fe on Fe/SiO₂ catalysts with uniform pore structure,the CO conversion rate and the selectivity of lower hydrocarbons increases,while the selectivity of higher hydrocarbons decreases.And the selectivity of CO₂ rapidly increases with the increase of the Fe loading.It's well known that the physicochemical property mutation of the supported catalysts is related to the monolayer dispersion threshold of their active components.Therefore,to study the effects of pore size and active metal Fe dispersion on the performance of the Fe/SiO₂ catalyst,the mono-layer dispersion threshold of Fe₂O₃ on the surface of SiO₂?0.09125 g Fe₂O₃/100 m² SiO₂?was measured by X-ray diffraction.