Study On Preparation Of ZrO₂/SAPO-34 Composite Catalysts And Their MTO Catalytic Performance

Since the extremely short lifetime of SAPO-34 in the MTO reaction??6 h?,the design and fabrication of a t-ZrO₂/SAPO-34 composite with micro-mesoporous system is proposed as a manner to promote SAPO-34 catalytic lifetime utilizing acid-base mesoporous ZrO₂ as a promoter via composite strategy,based on the principle of reaction temperature and ethylene on the formation of coke deposition.The formation of B acid-L acid and B acid-L base sites are beneficial to the dissociative adsorption of methanol and inhibition of carbon deposition in the lower reaction temperature.The effects of different composite preparation methods on the structure and properties of t-ZrO₂/SAPO-34 composite catalysts and the catalytic performance of MTO process were studied systematically.The structure and properties of the composite catalysts and the MTO process of the ZrO₂ phase state,the mass ratio,the t-ZrO₂ coating gelation time,the fineness of t-ZrO₂ powder,the calcination temperature and the calcining heating rate were further investigated.The effect of catalytic performance.The structure activity relationship of t-ZrO₂/SAPO-34composite catalyst was revealed by means of XRD,FT-IR,SEM,TEM,BET,NH₃-TPD,NH₃-IR and CO₂-TPD.The results show that the composite preparation method and technological conditions have great influence on the structure and MTO catalytic properties of the t-ZrO₂/SAPO-34 composite catalyst.The liquid phase precipitation coating method,the coating phase of t-ZrO₂ and the SAPO-34 as the nuclear phase,the SAPO-34/t-ZrO₂ catalyst could not form the coated composite phase,and the hydrothermal coating method is used for SAPO-34 is coated with t-ZrO₂ as nuclear phase at 450?for 2 h,t-ZrO₂:SAPO-34 mass ratio 1:1,t-ZrO₂coating gel time 24 h,t-ZrO₂ powder fineness 200 mesh,calcination temperature550?,and calcining heating rate 5°/min to form compound phase and meso-micropore structure(The micropore area is 112.91 m²·g^-1,the mesoporous surface area is 176.02 m²·g^-1,the total specific surface area is 288.93 m²·g^-1,the total pore volume 0.19 cm³·g^-1).Meanwhile,it has B acid(1430 cm^-1,1450 cm^-1),L acid(1630 cm^-1)and L base center?The total acid amount of 0.35 mmol/g,total base content reached 0.11 mmol/g?.Under the conditions of atmospheric pressure and reaction temperature 380?,the composite catalyst showed a longer catalytic life of1130 min.Compared with single SAPO-34 zeolite,the catalytic lifetime is prolonged by 770 min.In order to reveal the carbon deactivation of composite catalyst,the carbon accumulation behavior of composite catalyst t-ZrO₂/SAPO-34 was studied.The effects of the reaction temperature and reaction time of MTO reaction on the carbon and physicochemical properties of the composite catalyst were investigated by means of UV-Raman,O₂-TPO,XRD,BET and NH₃-TPD,and the comparison and analysis of SAPO-34 molecular sieves and compound catalysis were made.The carbon and oxygen consumption after the reaction of the chemical agent to 6 h.The results show that,with the increase of reaction temperature,the carbon species from 330⁴20?to deactivation gradually transform from adamantane to large molecular size methyl substituted benzenes.Compared with the pre reaction composite catalysts,the crystallinity,specific surface area and total acidity of the catalyst decreased significantly at different temperatures to deactivation,but at 380?reaction.When deactivated,the composite catalyst still has high crystallinity,and the total oxygen consumption of carbon deposition is the lowest,5.49 mmol/g.At 380?,the carbon species of methyl substituted benzene increased gradually with the reaction time,but the carbon species decreased gradually after the reaction to 12 h,and the oxygen consumption of the reaction to 12 h increased by 62.50%compared with the initial reaction,but the oxygen consumption of the reaction to 20 h was 33.90%lower than that of the 12 h.The composite catalyst has similar carbon accumulation to the single SAPO-34,but the oxygen consumption of the composite catalyst is reduced by66.72%compared with SAPO-34 when 6 h?SAPO-34 is deactivated?.The effects of different reaction temperature,feed velocity,water alcohol molar ratio and nitrogen flow rate on the conversion of methanol,the selectivity of low carbon olefin and the reaction life of t-ZrO₂/SAPO-34 composite catalyst were investigated by single factor and response surface method.The results show that the conversion rate of methanol,the selectivity of low carbon olefin and the catalytic life of the catalyst are 100%,90.54%and 1130 min,respectively,at normal pressure,380?of reaction temperature,1 g of the loading capacity of composite catalyst,2 h^-1of feed velocity,2:1 of water alcohol mole ratio and 20 mL·min^-11 of nitrogen flow.