Tailoring the performance of Pt/TiO2 catalysts in the dehydrogenation of perhydrobenzyltoluene
Résumé
Introduction Today hydrogen is considered a key energy vector in the transition to renewable energy. As a method of hydrogen storage Liquid Organic Hydrogen Carrier (LOHC) technology, particularly the perhydrobenzyltoluene (H12BT)-benzyltoluene (H0BT) couple, is gaining significant attention for its favorable physical properties and competitive H2 storage density (6.2 wt%). To release hydrogen from LOHCs, Pt catalysts are currently used both in industry and academia. Our study explores the effect of TiO2 supports on the structural and catalytic properties of Pt nanoparticles (NPs), intending to achieve higher activity and selectivity compared to a commercial Pt/Al2O3 catalyst. Materials and Methods TiO2 supports were selected from commercial sources, some of which were subjected to heat treatment to change the ratio of polymorphs in the sample. TiO2 supports are named Ax, where x stands for the percentage of anatase phase in the titania. The 0.4 wt% Pt/γ-Al2O3 catalyst was provided by Heraeus. Pt/TiO2 catalysts were synthesized via incipient wetness impregnation using Pt(NH3)4(NO3)2 precursor with subsequent calcination and reduction treatments. The loading of Pt was 0.5 wt%. Catalytic tests were performed in a glass reactor with continuous removal of hydrogen connected to a GC-TCD. Recycling tests were performed in a stainless steel autoclave connected to a micro-GC. Reaction conditions : n(Pt)/n(H12BT) = 9*10-5, 260 °C, 4 h. Results and Discussion The preparation of Pt/Ax catalysts resulted in the formation of Pt NPs of 1.0-1.6 nm in average size. The performance of the catalysts depends on the nature of the support as well as on the structure of the particles. Compared to Pt/Al2O3, Pt/TiO2 catalysts show higher productivity (P) and degree of dehydrogenation (DoD), except for Pt/A100. In particular, using Pt/A0, 47 % of DoD was achieved with an initial productivity of 2.2 g(H2)/g(Pt)/min, while for Pt/Al2O3 the values of DoD and P are 35 % and 1.4 g(H2)/g(Pt)/min. As for the selectivity, Pt/TiO2 catalysts lead to less methylfluorene (MF) side-product. Namely, at an H0 yield of 11 % using Pt/Al2O3, the MF yield reaches 0.40 %, whereas with Pt/A0 only 0.09 % MF is formed. Selectivity improvement can be ascribed to both support and NP properties. Firstly, MF production can be promoted by acidic sites. Titania has lower acidity than alumina and rutile is less acidic than anatase1. Currently, FTIR measurements with a pyridine probe are being conducted to rationalize this behaviour. Secondly, undercoordinated Pt sites (steps, corners) can strongly adsorb H0BT, which can be subsequently converted into MF2. CO-DRIFTS analysis confirmed that the most selective catalyst has the lowest fraction of undercoordinated Pt. During the recycling, a mild deactivation of the Pt/A0 catalyst was observed. A post-characterization and a regeneration of the catalyst will be presented during the conference. References 1.H. Li, M. Vrinat, G. Berhault, D. Li, H. Nie and P. Afanasiev, Mater. Res. Bull., 2013, 48, 3374–3382. 2.F. Auer, A. Hupfer, A. Bösmann, N. Szesni and P. Wasserscheid, Catal. Sci. Technol., 2020, 10, 6669–6678.