Deep desulphurization of diesel fuels on bifunctional monolithic nanostructured Pt-zeolite catalysts

The preparation of Pt-zeolite catalysts, including choice of the noble metal precursor and loading (1.0–1.8wt.%), was optimized for maximizing the catalytic activity in thiophene hydrodesulphurization (HDS) and benzene hydrogenation (HYD). According to data obtained by HRTEM, XPS, EXAFS and FTIR spectroscopy of adsorbed CO, the catalysts contained finely dispersed Pt nanoparticles (2–5nm) located on montmorillonite and zeolite surfaces as: Pt0 (main, νCO=2070–2095cm−1), Ptδ+ (νCO=2128cm−1) and Pt2+ (νCO=2149–2155cm−1). It was shown that the state of Pt depended on the Si/Al zeolite ratio, montmorillonite presence and Pt precursor. The use of H2PtCl6 as the precursor (impregnation) promoted stabilization of an oxidized Pt state, most likely Pt(OH)xCly. When Pt(NH3)4Cl2 (ion-exchange) was used, the Pt0 and hydroxo- or oxy-complexes Pt(OH)62− or PtO2 were formed. The addition of the Ca-montmorillonite favoured stabilization of Pt+δ. The Cl− ions inhibit reduction of oxidized Pt state to Pt particles. The Pt-zeolite catalyst demonstrated high efficiency in ultra-deep desulphurization of DLCO. The good catalyst performance in hydrogenation activity and sulphur resistance can be explained by the favourable pore space architecture and the location and the state of the Pt clusters. The bimodal texture of the developed zeolite substrates allows realizing a concept for design of sulphur-resistant noble metal hydrotreating catalyst proposed by Song [C. Song, Shape-Selective Catalysis, Chemicals Synthesis and Hydrocarbon Processing (ACS Symposium Series 738), Washington, 1999, p. 381; Chemtech 29(3) (1999) 26].