The Study Of AlOOH Structures And Catalytic Properties

In our previous work,CuZnAl catalysts were prepared by complete liquid-phase technology,which was present by our independent innovation.It was found that the existing form of Al was a kind of meta-stable phase AlOOH,rather than the conventional ?-Al2O3.AlOOH was a kind of incomplete crystallization of alumina hydrate with a special double layer structure,which showed the properties of high interfacial free energy,large porosity and surface area as well as good dispersion.At present,AlOOH was mainly used for the preparation of ?-Al2O3 precursor,as adsorbent and catalyst support.However,AlOOH as catalyst was rarely reported.In our previous work,Al OOH was prepared separatly and then were mixed with industrial methanol synthesis catalyst C302,and the resulted composite catalysts were investigated for CO hydrogenation reaction.An interesting found was that composite catalysts had high selectivity for C2+OH.Nevertheless,the corresponding mechanism was still unclear.In order to explore the catalytic performance of AlOOH,in this paper,several different structures of AlOOH synthesized by hydrothermal method were used for methanol with CO or syngas reactions to study the effect of AlOOH structure on the reaction performance and to speculate the catalytic mechanism of AlOOH.And on this basis,AlOOH were further prepared by different methods,followed by loading with C302 by layers in a fixed bed reactor.The catalytic performance of AlOOH and C302 composite catalysts was evaluated in CO hydrogenation reaction and the influence of different preparation methods on the properties of CO hydrogenation reaction was investigated.The main conclusions were summarized as follows:1.At normal pressure,AlOOH,as the catalyst for methanol with CO or syngas reaction,showed weak activation ability to CO but had strong methanol dehydration ability.The introduction of methanol and syngas simultaneously affected the adsorption of methanol on AlOOH,thus producing an effect on the conversion rate.2.The pressure showed obvious influence on the product distribution of methanol with CO or syngas reaction over AlOOH catalyst.At normal pressure,products were mainly dimethyl ether and hydrocarbons,while under high pressure(4 MPa),products were mainly acetaldehyde and dimethyl ether.Results showed that AlOOH catalysts which had higher crystallinity,larger aperture,extensive CO dissociative adsorption center and suitable acidity and basicity significantly promoted the production of acetaldehyde.3.According to the characterization and activity evaluation results,it could be speculated that the acetaldehyde was generated by the coupling of CH3 and HCO,which confirmed that AlOOH could promote the carbon chain growth.4.Different preparation methods dramatically affected the AlOOH structures and the product distribution of layered composite catalysts.After hydrothermal treatment,the crystallinity of AlOOH was improved,the layer structure was more complete,and the surface acidity of Al OOH was changed obviously.AlOOH catalyst with high activity and C2+OH selectivity was closely related to complete crystal forms,obviously preferred orientation and appropriate acidic-basic sites.5.Different loading ways of the catalyst had significant effects on the catalytic performance.Mechanical mixing was more conducive to the formation of C2+OH than layered composite,indicating that the synergy of AlOOH and CuZn components had a certain influence on the generation of C2 +OH.