The Effect Of Preparation Environment Of Precursor On Catalytic Structure And Performance Over Catalyst For One-step Synthesis

As the economy develops continuously,the problems on energy and environment have become increas ingly prominent.Based on the"rich coal,poor oil and low gas"energy structure,Coal-based fuels has gradually become a hot topic in the energy field.With its unique phys ical and chemical properties,Dimethyl Ether,produced by syngas has attracted more and more attentions.It is considered as a environmentally friendly clean fuel s ince it has the characteristic of high cetane number,low CO,NOx and PM emissions when burned.The catalyst produced by the traditional method is easily inactivated in slurry bed reactor,however,our research team has successfully solved the problem of"Complete Liquid Phase Method."But,it can also be improved on Dimethyl Ether selection,CO conversion,and product additional value.The producing environment of the precursor will directly affect its property and structure,thus determine the catalytic property.The Sol-Gel technology is widely used in the manufacturing of the catalyst due to the advantages of small size,good dispersibility,high purity,and easy contro l of the ratio of reactive ions.However,it may cause turbidity or even precipitation on account of complex process and improper control during manufacturing process.The gelling environment plays an important role in colloid forming and catalytic properties.Based on the"Complete Liquid Phase"process,we designed a series experiments with the aim of"Three Improvements"begin with the precursor's gel formation environment.In terms of improving Dimethyl Ether selection,we have added different amount of ammonia in the gelling process to explore the influence of precursor gel pH to DME's selection.In addition,we have also observed the effect of the ammonia injection time and methods.In terms of the CO conversion,we have observed the effect of different injection amount to CO conversion by adding different kinds of complexing agents?citric acid,acetic acid,acetylacetone?in the gelation process.In terms of increasing product additional value,we have observed the influence of the raw material on the product distribution.By us ing XRD,NH₃-TPD-MS,H₂-TPR,N₂-adsorption test,XPS,characterization methods,we can draw the following conclusions:1?When the gelling pH is neutral,DME selectivity increased 11.78%to73.31%.After changing the ammonia injection time,the CO conversion has been greatly improved.Besides,great changes has taken place in the product distribution by changing ammonia injection method.Among them,the selectivity of the Dimethyl Ether catalyst produced by co-current method has been greatly reduced,while the CO₂ selectivity has reached 35.28%,and the total hydrocarbons have increased six times which is up to 18.27%.The small particle size of Cu⁰,the increase of reducible Cu species,the decrease of Mean pore-size,and the improvement of the dispersion of Zn on the surface of the catalyst are beneficial to the improvement of catalytic activity.2?When adding citric acid during gelation process,CO conversion has increased 7.24%to 67.8%.Due to the complexation,the interaction between Cu species and other components has increased greatly,and the carbon content on the catalyst surface decreases significantly which contributed to the formation of small pore size catalysts.With the increase of the citric acid amount,there is a large amount of reducing gas decomposed during the heat treatment and the Cu⁺on the catalyst surface is basically reduced in the heat treatment stage.When the citric acid amount up to 0.2 mol,the number of weak acid on the catalyst surface will increase significantly,however,there is no significant increase in dehydration performance,which indicate that the dehydration performance of the catalyst is not only related to the weak acid but also the strong acid on the surface.3?When the molar ratio of gelled CuZn Al is 2:1:2,the product with high added value"ethanol"will appear in the product.With the decrease of Al content,the grain size of Cu⁰ has increased during the reaction from beginning to the end,and the reaction activation has also decreas ed significantly.By reducing the input amount of Al in raw material,the amount of reducible Cu in the catalyst keep increasing,and the acidity of the weak acid has increased gradually.