Surface Control And Hydrodesulfurization Performance Of Mesoporous Titania-based Catalysts

As a new catalytic support, TiO2exhibits a promising application potential in manyreactions of both environmental and industrial importance, such as hydrodesulfurization(HDS) selective catalytic reduction and low-temperature oxidation. TiO2has a “stronginteraction” with active species, which can improve the unit activity of catalyst. However,there are few reports on widely industrial applications of TiO2as catalytic support now.Conventional TiO2has many defects on its structure, such as small surface area (<10m2/g),low thermal stability (anatase transforms to rutile at550oC) and poor mechanical properties(crush strength:1~2N/mm). It is generally considered that low surface area of TiO2can causea decrease in the amount of active sites, resulting in a poor catalytic performance. Therefore,numerous works are devoted to improving various structural properties of TiO2to promote itscatalytic performance.Based on the previous works of mesoporous TiO2whiskers, we tried to improve thecatalytic activity of mesoporous TiO2-supported catalysts by three ways. Simultaneously, theproperties of supports and catalysts were characterized by means of Raman, N2adsorption,XRD, FT-IR and SEM techniques. An investigation into the HDS performance ofTiO2-supported catalysts of dibenzothiophene (DBT).Glucose as the predecessor of carbon source, MoNi/TiO2-Cg catalyst were prepared byincipient impregnation. It indicated that carbon modification was indeed beneficial to improveHDS performance. The incorporation of carbon could inhibit the TiO2phase change andimprove the crystallinity of TiO2during the heat treatment. Simultaneously, it promots theformation of β-NiMoO4, which is easier to be reduced than α-NiMoO4and generally showsbetter catalytic properties. Further increase in the carbon content, the HDS performance ofcatalysts did enhance the catalytic performance. When the carbon loading was5.0wt%,NiMo/TiO2-Cg catalyst showed the highest activity of95.7%while88.7%for NiMo/TiO2.By adopting molecular self-assembly technique, the surfaces of mesoporous TiO2whiskers were carbon modified with18alkyl phosphate(C18P) as carbon source. This methodhas been considered to form a carbon heterogeneous self-assembled monolayer on titaniasurface in flowing N2. A novel MoNi/TiO2-C catalyst was prepared by the incipient wetnessimpregnation method. An investigation into the HDS performance of MoNi/TiO2-C ofdibenzothiophene (DBT), and a detailed examination of the effect of different carbon contents (0.25-3wt.%) was studied. Results showed that MoNi/TiO2-C exhibited more excellentcatalytic activity at a low temperature and pressure. Under relatively mild conditions of280oC,2MPa, LHSV4h-1and H2/feed ratio400Nm3/m3, the addition of carbon content to0.5wt.%, the DBT conversion of MoNi/TiO2-C could reach up to100%. The improved activity ofthe novel catalysts was attributed to the carbon surface modification, which changed surfacechemical properties of pure TiO2. Additionally, existing carbon species weakened theinteraction between the support(TiO2) and the resultant (H2S), and H2S could be desorbedfrom the surface of TiO2-C easily.Finally, nano/micro-composite TiO2(TiO2-m) derived from K2Ti2O5was synthesized viaion-exchange. The SEM results showed that the prepared TiO2-m supports were shaped innano-scale particle and micron-sized whisker morphology. Supported MoO3/TiO2catalystwere prepared by incipient impregnation. An investigation into the HDS performance ofMoO3/TiO2of DBT, and the morphology of TiO2supports is an important factor concernedfor its HDS performance. The effect of TiO2whisker contents, MoO3contents and NiO onHDS activity of titania-based catalysts was studied. Compared with pure morphology controlsamples, the HDS tests indicated that Mo catalysts supported on TiO2-m materials had thebest HDS catalytic activity under relatively mild reaction conditions. The incorporation ofTiO2whisker and NiO could enhance the catalytic performance. When the MoO3loading was10wt%, MoO3/TiO2-1catalyst showed the highest activity.