Preparation And Performance Of High-activity Zeolitic Catalysts For Catalytic Reforming At Low Temperature

Catalytic reforming is a refining process that produces aromatics,high-octane gasoline and hydrogen through the rearrangement of hydrocarbons.The commercial reforming catalyst is alumina with element Cl and highly dispersed Pt.Although this catalyst has been widely used,the element Cl is easy to drain.It not only causes equipment corrosion,but also needs continuous chlorine supplementation to maintain acidity.Therefore,zeolitic catalysts with sufficient acidity and without chlorine supplementation have attracted wide attention.Conventional reforming catalyst compensates for the loss of activity by increasing the reaction temperature,but it will not only reduce the Liquid Yield,but also increase the energy consumption and damage the equipment.Zeolitic reforming catalysts can improve the aromatization activity of straight-chain alkanes,but the raw materials and process parameters used for evaluation are far from industrial reality in current studies.Thus,it is necessary to continue to explore zeolitic reforming catalysts with high activity,selectivity and stability at low temperature.In this paper,Zeolite L and Zeolite Y with different cations were obtained by the ion exchange method.Pt was used as the active metal,and L-type and Y-type reforming catalysts were prepared by two preparation sequences.The physical and chemical properties of the zeolitic reforming catalysts were investigated by more than ten characterization methods such as XRD,NH₃-TPD,N₂ physical adsorption and desorption,Py-IR,H₂-TPR,SEM,STEM and compressive strength testing.These can also analyze pore structure,acidity and metallic state of catalysts with different sequences of binder additions.Using hydrofining naphtha as raw material,the reaction performance of all zeolitic catalysts were investigated on a 100ml fixed bed reactor at450°C which lower than the industrial reaction temperature.At the same time,a domestic commercial alumina reforming catalyst was selected as reference agent.The activity of the catalysts were compared with the content of aromatics in the liquid product（referred to as Aromatic Content）,and the comprehensive performance was measured by the product of Aromatic Content and Liquid Yield（referred to as Aromatic Yield）.The results show that the addition of the binder doesn?t destroy the crystal structure of zeolite,but can increases the mesopore volume,changes the acid distribution,and improves the strength of the catalyst.It was shown that the sequence of preparation also affects the catalytic performance of catalysts.The comparison shows that the Pt in Pt/ML-EI and Pt/MY-EI（Extruding before Impregnating）is highly dispersed,the aromatization activity and catalytic comprehensive performance of Pt/ML-EI are better than that of Pt/ML-IE and Pt/MY-IE（Impregnating before Extruding）.The rare earths Ce and La can change acidity without changing the crystal characteristics,increase the acid content and improve dehydrogenation activity of the catalysts.Then promote the synergy between the metal center and acid center,so the Aromatic Content is increased.In addition,the amount of carbon deposits on the catalyst is reduced.Using naphtha as raw material,the reaction evaluation of all catalysts was carried out under the conditions of 0.7 MPa,and LHSV of 2 h^-1.Liquid Yield,Aromatic Content and Aromatic Yield of the commercial reforming catalyst are88.7 wt%,47.8 wt%and 42.3 wt%at 450°C,and 79.0 wt%,71.0 wt%and 56.1 wt%at 490°C.For the L-type catalysts,the Liquid Yield,Aromatic Content and Aromatic Yield of Pt/Ce L-EI are 81.6 wt%,46.9 wt%,and 38.2 wt%at 450°C,and the values of Pt/La L-EI are 76.8 wt%,54.3 wt%,and 41.7 wt%at 450°C.The comprehensive performance of the two L-type catalysts are similar to commercial reformers at the same temperature.For the Y-type catalysts,the Liquid Yield,Aromatic Content and Aromatic Yield of Pt/La Y-EI are 66.0 wt%,60.5 wt%,and 39.9 wt%at 450°C,and the values of Pt/Ce Y-EI are 65.1 wt%,78.4 wt%,51.0 wt%at 450°C.Both the two Y-type catalysts are more active than the commercial catalyst at 450°C,and the activity of Pt/Ce Y-EI at 450°C was even higher than that of the commercial catalyst at 490°C.In summary,Pt/Ce Y-EI has high application value and prospects.