| Maleic anhydride (MA), manufactured by benzene or butane, was the third-largest anhydride material. The molecule of maleic anhydride is a cyclic compound composed of a C=C bond, the two C=O bands, and a C-O-C functional groups. The hydrogenation of MA can produce a series of valuable fine organic chemicals, such as succinic anhydride (SAH), y-butyrolactone (GBL),1,4-butandiol (BDO) and tetrahydrofuran (THF), etc. All these products are significant intermediate chemicals and solvents in oil processing, mechanical, war industries, farm chemicals, textile industries and plastics. The preparation of active and selective catalyst for maleic anhydride hydrogenation was the hot issue of study. In the open literature, the activity and selectivity of catalyst for maleic anhydride hydrogenation are improved by adjusting the morphology, size, metal-support interaction, and electronic configuration of active component. Little research was focused on the effect of support.There are many works in which certain polymorphic ZrO2supported catalysts exhibited superior performance. The catalytic performance of ZrO2or ZrO2-based catalyst can be deeply affected by the ZrO2polymorphs because the surface physical-chemical properties with ZrO2polymorphs are very different. To our knowledge, the research of ZrO2polymorphs effect in hydrogenation catalyst was focused on small molecules CO and CO2hydrogenation, there is not research work dealing with the study of ZrO2polymorphs influence on the catalytic performance of catalysts in maleic anhydride or other organic molecules hydrogenation.Based on the preliminary studies of our group, the effect of ZrO2polymorphs on the catalytic performance of Ni/ZrO2catalyst for maleic anhydride hydrogenation was studied. The surface and textural properties of catalysts were characterized by XRD、 H2-TPR、H2-TPD、NH3-TPD、CO-TPSR and in-situ DRIFTS was employed as probe reaction. The impact mechanism of ZrO2polymorphs on the catalytic performance of Ni/ZrO2catalyst was speculated. This subject is beneficial to understand the support of Ni-based catalysts on maleic anhydride hydrogenation, and developing high performance catalyst for selective hydrogenation of maleic anhydride.The main results were obtained as follow: 1. The hydrogenation of MA in liquid phase was studied over Ni-based catalysts supported on m-ZrO2and t-ZrO2respectively. All these results demonstrated that the selectivity to GBL of Ni/t-ZrO2catalysts were higher that of Ni/m-ZrO2catalysts. The major reason is there is more unsaturated coordinatively of Zr4+cations existed on Ni/t-ZrO2catalyst surface. It accept lone pair electrons of oxygen atom of C=O. The synergetic effect between Zr4+and Ni0prompted the hydrogenation of C=O band. More unsaturated coordinatively of Zr4+-O2-acid-base centers and unsaturated coordinatively O2-basic centers were detected on Ni/m-ZrO2surface. The presence of these centers reduced the probability of collision between the catalyst and the C=O band. Compared with Ni/t-ZrO2catalysts, the activity for C=O hydrogenation was reduced obviously.2. In order to reveal the effect of ZrO2polymorphs on catalytic performance of Ni/ZrO2catalyst, the paper further study the influence of ZrO2polymorphs changes during the heat treatment process on catalytic performance of Ni/t-ZrO2catalysts when the same Ni loading conditions. The results show that when the calcination temperature range from573K to673K,t-ZrO2on the surface of the catalyst and the selectivity for GBL is almost maintain a constant. As the calcination temperature further increased to773K or873K, the catalytic activity for83%droped down to53%and50%. The reason for this phenomenon is that t-ZrO2convert to m-ZrO2on the surface of the catalyst during the heat treatment. The unsaturated coordinatively Zr4+centers gradually evolved into a unsaturated coordinatively Zr4+-O2-acid-base centers and unsaturated coordinatively the O2-base center. Therefore, ZrO2polymorphs have a greater influence on catalytic performance of Ni/ZrO2catalyst. |
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