| Developing and applying the efficient catalyst in the chemical production process should follow the principles of "green chemistry" and "atom economy" to address both increasingly consumption of resources and environmental issues,with an aim of promoting continuous improvement of existing technologies and creating new procedure with high efficiency and low emissions.The structure-activity relationship between surface structure and catalytic properties of the catalyst has been studied for several decades,have abudance accumulation.Over the past two decades with the rapid development of nanotechnology making it possible to design and control the surface structure of the catalyst on the nanoscale,heterogeneous catalysts with a high proportion of specific surface can be prepared,which can greatly improve the catalytic activity and selectivity.Gamma alumina itself is a good solid acid catalyst and also acted as the most important high specific surface catalyst support,is a very important catalytic material.The mainly expose outer plane for industrial gamma alumina is(110)plane,Therefore,it has important significant theoretically and practically to prepared and characterized of gamma alumina whose mainly expose plane is higher energy(111)plane.In this paper,we have prepared alumina nanotubes with mainly exposure of(111)plane based on the existing working in our group.Meanwhile,we have used different characterization methods to systematic study its plane-dependent physical and chemical properties and explore the relationships between the exposed planes of support and the catalytic performance after metal and oxide loading and then obtained a series of innovative and useful results.The contents are summoned below:(1)The ?-Al2O3 nanotubes preferentially exposing(111)planes is prepared by a"bottom-up" method using oleic acid as a protective agent of crystal surface,and then compared with the conventional ?-Al2O3 whose exposed plane is(110)to obtain the surface structure differentiation between this two kinds of alumina.The examination of surface structure and catalytic performance of ?-Al2O3 nanotubes confirms that?-Al2O3 nanotubes preferentially expose the(111)planes,which have higher density of hydroxyl,higher acidic density and higher strength of acid compared with(110)planes.Finally,a possible preparation mechanism of alumina nanotubes is proposed and the results of DFT calculations prove the rationality of the preparation mechanism.(2)The interaction between the high energy(111)crystal surface and the palladium metal and its effect on the performance of acetylene hydrogenation are studied.Supported metal catalysts(Pd/?-Al2O3)with different loadings are made using the above-prepared ?-Al2O3 nanotubes with preferentially exposed(111)planes and the conventional ?-Al2O3 with preferentially exposed(110)planes as support,respectively.The results showed that the interaction between the Pd and ?-Al2O3(111)plane is much stronger can enable Pd grown on Al2O3 surface structure.The results of theoretical calculations demonstrate that the adsorption energy of Pd4 cluster on?-Al2O3(111)plane is stronger,which makes the improvement of palladium dispersion,furthermore,the d-band center changed.There is greater difference in adsorption energies of ethylene,acetylene to the Pd on(111)plane,these makes the different catalytic properties to conventional alumina,has a higher conversion of acetylene and high selectivity of ethylene.(3)The interaction between the high energy(111)crystal surface and the loaded titanium oxide and its interactions with the catalytic hydrogenation are studied.A relatively stable TiOx/Al2O3 catalyst is prepared by a "liquid ALD" method and applied to the gas phase selective hydrogenation of acetylene reaction which founding comparable catalytic performance as metal supported catalyst.The catalysts are characterized by a series of characterization which indicated that the Ti(?)species on catalyst surface is the activity center of hydrogenation reaction.Owing to the high energy of ?-Al2O3(111)plane,the interaction with TiO2 is much strong.After reduction at high temperature,the TiO2 highly dispersed on surface of ?-Al2O3 and mainly reduced to low valence titanium,could be capable of adsorbing and dissociating hydrogen molecules and thus has better selective hydrogenation performance.While TiO2 is supported on conventional alumina,after high temperature reduction,it is easy to gather into small particles,can not easily be reduced,the active constituent Ti(?)species at a low concentration and therefore poor hydrogenation performance.This study will expand application of TiO2-based catalyst to the field of heterogeneous hydrogenation and open up the application to hydrogenation of other functional groups with good new ideas.(4)A high-performance catalyst TiOx/Al2O3 is obtained by dispersing TiO2 on a special alumina support for the MPV reduction of CAL to COL in an exclusive selectivity.Systematic studies indicated that the content of Ti(?)contribute significantly to the high selectivity of catalyst.We believe that the highly efficient and easily prepared catalyst has great potential of application in other ?,?-unsaturated aldehydes MPV reductions and some other Lewis acid catalyzed reactions,and that the design of other heterogeneous catalysts for MPV reduction. |
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