Studies On Preparation And Catalytic Performance Of High Dispersion Pt Based Catalysts

Methane reforming with carbon dioxide has important scientific significance on mitigating the energy crisis and protecting the environment not only because it yields syngas with low H2/CO(<1) desirable for Fischer-Tropsch synthesis and other depth conversion, but also because it is beneficial to control the emission of greenhouse gas CH4 and CO₂. Owing to the rapid deactivation resulted from carbon deposition and loss of active components on the conventional Ni-based catalysts, the noble catalysts with higher activity and stability have been attracting enormous interest. This paper is focused on the preparation of highly dispersed Pt-based catalysts by support modification, improvement of preparation method and addition of promoter, which can reduce the cost of Pt, improve the stability and resistence to carbon deposition of the catalysts.The optimal conditions of modified nano-MgO support which is prepared by environmental friendly ion exchange resin method are obtained from monofactor experiment study for the first time as follows: under continuous stirring of 400 r/min, 100 mL MgCl2 solution of 0.2 mol/L is added to 250 mL 201×7 strong-base anion exchange resin to react for 8 h at 323 K, the Mg(OH)2 hydrogel is obtained after vacuum filtrating and washing, and then calcined at 673 K for 6 h under nitrogen atmosphere. The obtained nano-MgO has a regular hexagonal lamellar morphology with an average diameter of 15 nm and SBET of 105.7 m2/g, which is suitable to act as Pt-based catalyst support.In order to investigate the effect of the support modification process on catalysts performance, a series of 0.8%Pt-3%CeO₂-3%ZrO₂/MgO catalysts are prepared by co-impregnation method, and their characterization and the performance of CO₂ reforming CH4 are investigated by activity measurement, XRD, SEM, BET and CO₂-TPD et.al. Experiment results reveal that the catalysts supported on Mg(OH)2 powder which is generated from Mg(OH)2 hydrosol after vacuum filtration and general drying at 393 K for 6 h have larger surface area and show higher Pt metal dispersion and catalytic activity.In order to investigate the effect of the impregnation order between the active component and promoter on catalyst performance, a series of 0.8%Pt-3%CeO₂-3%ZrO₂/MgO catalysts are prepared by seq-impregnation method. XRD and activity evaluation results indicate that, when Pt is impregnated firstly, and then promoter CeO₂ and ZrO₂ which can contribute to the improvement of metal-support interaction, the prepared catalysts 0.8Pt-3Ce3Zr/MO800-IE and 0.8Pt-3Ce3Zr/MO800 have better dispersion of Pt metal on MgO, thus show high catalytic activity. However, the catalytic activity reduces when the impregnation order is opposite, because some pore channels of MgO may be blocked, especially in the case of large amount of ZrO₂. When the catalysts are prepared using the MOH(GD)-IE as the support, the optimum mass ratio of CeO₂ to ZrO₂ promoter is 1 : 0.33. According to the CO₂-TPD result, this is mainly because the large additive amount of CeO₂ results in the increase of basic sites of support, consequently, the reforming reaction is easily performed.