Effect of TiO2-Al2O3 support surface properties on active phase structure and hydrodenitrogenation performances of the corresponding NiWS supported catalysts

To explore the effect of the support surface properties on the active phase structure and the hydrodenitrogenation (HDN) catalytic performance of the corresponding hydrotreating (HDT) catalyst, three kinds of TiO2-Al2O3 supports with a Ti/Al molar ratio of 1 but different Ti-Al composite result were prepared by the following methods: the mechanical mixing method (T + A), the ion-exchange method (T/A) and the in-situ synthesis method (TA). The Ti-Al composite results of the supports were characterized by XRD, FTIR, SEM-Mapping and N2 physical adsorption-desorption techniques and the properties of the NiW supported catalysts were determined by XRD, H2-TPR, HRTEM and XPS. The results show that the surface properties of TiO2-Al2O3 composite supports can be modulated by changing the Ti modification method. Among all the three methods, the in-situ synthesis method can achieve the atomic mixing of titanium and aluminum elements to maximize the Ti-O-Al bonds, followed by the ion-exchange method, and finally the mechanical mixing method. Accordingly, the number of Ti -O-Al bonds in the support determines the dispersion, stacking and sulfurization of the active phase. When more Ti-O-Al bonds are present in the support, the higher the dispersion and sulfurization degrees of the active metals and the stacking layer number of the NiWS active phase in the catalyst, thus exhibiting higher HDN activity both for basic and non-basic nitrides. In addition, Ti3+ species can be generated when enough Ti-O-Al bonds are present in the support surface, which also enhance the promotion of the sulfidation degrees of the active metal and the formation of CUS and thus further improve the HDN activity. Generally, the in-situ Ti modification method was considered to be the favorable method for preparing highly active HDT catalysts due to its excellent Ti-Al composite surface properties.