| Petroleum,as the non renewable resource,its consumption is continuously increased in recent years.But many chemicals originated from petroleum industry have become the essentials in our daily life.As a result,there is a strong trend to manufactory chemicals by using biomass-derived resource.Acrylic acid is currently produced through two step oxidation of propylene,however,the process is complicated and different catalysts need to be used.One step partial oxidation of propane to acrylic acid is highly desirable and has received numerous attentions in recent years,and the researches are particularly focused on the MMO type catalyst whose nature is very sensitive to preparation parameters and the "window" of synthesizing active catalyst is rather narrow.It is of highly social and economic importance to transform the over-produced goods and low-value by-product(such as acetic acid/methyl acetate)into the significantly value-added bulky chemical(such as acrylic acid/acrylate).Regarding the energy status of our country,it is technically attractive to convert acrylic acid and acetic acid toward acrylic acid through aldol condensation reaction.VPO catalyst is a kind of complex catalyst system,and its structure and property is influenced by quite a few factors.Applying the vanadium phosphorus oxide type material as a general platform,one can make acrylic acid through the reaction routes of aldol condensation of acetic acid/methyl acetate with formaldehyde and following selective dehydration.In terms of the nature of target reactions,the integrated modification strategy of preparation chemistry is employed,particularly the controllable activation manner,and employing support materials.Both surface and bulk characteristics of the vanadium phosphorus oxide can be effectively tuned,especially on the aspects of phase constitution,surface P/V and V5+/V4+ratios,and acid-base as well as oxidation-reduction characters.The study of this thesis would extend a base for developing the talented VPO catalyst and the renewable and efficient technology of acrylic acid production.Potentially,supported VPO catalyst has advantages over the unsupported ones,including better heat transfer character,larger surface to volume ratio of active component,better mechanical strength,and controllable catalyst textures.In this thesis,the support materials of SiO2,TiO2,Al2O3,and ZrO2 have been employed in attempt to load VPO species via a wet-milling approach.Catalyst activation was found to critically determine catalyst structure and composition,especially the vanadium oxidation states and their relative contents.A ZrO2 supported VPO catalyst activated in butane-containing atmosphere showed better performance(a yield of approximately 63%).Catalyst activation in an atmosphere containing 0.3-0.6%butane is favorable for activity enhancement.The operation parameters,including reaction temperature,space velocity,and oxygen content in reaction feed,are systematically optimized on the ZrO2 supported catalyst.The highest(AA+MA)formation rate of 60?mol gcat-1 min-1 is achievable.The characterizations by means of XRD,Raman,H2-TPR,XPS clearly revealed that the factors such as higher V5+/V4+ratio,better redox cycle between V5+ and V4+,and higher density of medium strong acid sites could account for the enhanced activity.The oxygen concentration dependence of carbon loss was analyzed and the results indicated that only slight carbon loss(less than 4%)would occur as long as the oxygen concentration was not beyond 3%in the feed.Significant carbon loss was observed with further increasing oxygen concentration.Co-fed oxygen improves catalyst durability at the expense of carbon loss.A binary oxide support of ZrO2-TiO2 was also tried to load VPO and the catalyst activity was found to increase with increasing ZrO2 fraction in the mixed oxide.However,no obvious synergetic promotion effect was observed by this binary oxide support. |
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