Stable Highly-Dispersed Supported Pt Reforming Catalysts

Supported Pt catalysts are one of the most important catalysts in the process of petroleum refining and petrochemical industry. At present, one of problems existing in catalytic reforming industry is that metal active centers easily gather and even sinter in the process of high temperature reaction leading to the decrease of activity. Therefore, designing stable dispersed catalyst is very important to solve the problem. In this paper a kind of stable highly-dispersed Pt reforming catalyst in order to realize the stability of the catalytic performance. This paper has carried on as follows:(1) MgAlSn-LDH is synthesized in situ on the surface of spherical Al2O3. The lattice parameter a of MgAlSn-LDH/Al2O3in the XRD and the lattice spacing of MgO of MgAlSn-LDO/Al2O3in the HRTEM verify that Sn has been introduced into the LDH layer. In XPS, compared to SnO2/Al2O3, Sn(IV) in MgAlSn-LDO/Al2O3is harder to be reduced, indicating Sn in the MgAlSn-LDH/Al2O3is confined by lattices. (2) PtCl62-is introduced by incipient wetness impregnation. Upon calcination-reduction of a PtCl62-/MgAlSn-LDH/Al2O3precursor, a highly stable dispersed Pt/Mg A IS n-LDO/Al2O3catalyst is obtained. According to STEM and XPS, we can infer that the interaction between Pt and Sn exists, which is verified by TPR. According to the STEM and HOT, compare the Pt dispersion of the catalysts after one oxidation-reduction cycle and two oxidation-reduction cycles to fresh catalyst, finding that the dispersion of Pt in Pt/MgAlSn-LDO/Al2O3catalyst is more stable than in PtSn/Al2O3catalyst. In the n-heptane reforming reaction, compare the catalytic performance of the catalysts after one oxidation-reduction cycle and two oxidation-reduction cycles to fresh catalyst, finding that selectivity of C1is unchangeable in the Pt/MgAlSn-LDO/Al2O3catalysts and selectivity of C1increases in the PtSn/Al2O3catalysts, which relates to the stable dispersion of Pt in the Pt/MgAlSn-LDO/Al2O3catalyst and the unstable dispersion of Pt in the PtSn/Al2O3catalyst.(3) The used catalysts after regerations in situ catalyze n-heptane reforming reaction, and are compared to fresh catalyst, finding that the Pt/MgAlSn-LDO/Al2O3catalysts after regerations could return to the level of the fresh catalyst, but the PtSn/Al2O3 catalysts could not, indicating the reusability of Pt/MgAlSn-LDO/Al2O3catalyst is better than PtSn/Al2O3catalyst.(4) The influence of different impregnating solvents and Pt precursors on Pt dispersion and stability of Pt dispersion in Pt/MgAlSn-LDO/Al2O3catalysts are studied, founding that (a) the Pt dispersion of catalyst prepared by CH3COCH3with weak polarity as impregnation solvent achieves95%, and the Pt dispersion of catalyst prepared by H2O with strong polarity as impregnation solvent is75%;(b) the Pt dispersion of catalyst prepared by Na2PtCl6before and after oxidation-reduction are around95%, and when the catalysts are prepared by [Pt(NH3)4](NO3)2and Pt(acac)2, the dispersion of Pt has fallen by31%and38%, respectively.