Sol–gel synthesis of Pt/Al2O3 catalysts: Effect of Pt precursor and calcination procedure on Pt dispersion

Pt/Al2O3 catalysts are used in a wide variety of reactions. Tailoring the catalyst structure is important in order to efficiently and effectively utilize the noble metal. In this work, the effects of Pt precursor (Pt(NH3)4Cl2, Pt(C5H5N)4Cl2, Pt(CH3NH2)4Cl2, or Pt(C4H9NH2)4Cl2) and calcination procedure (heating rates of 2 °C/min or 10 °C/min in different atmospheres) have been investigated for 1.5 wt% Pt/Al2O3 catalysts prepared by sol–gel synthesis. After drying, calcination, and reduction, the Pt dispersion was measured by H2 chemisorption. The catalyst structures were characterized using X-ray diffraction, N2 adsorption, and transmission electron microscopy. The Pt precursors as well as the calcination procedures influenced the Pt dispersion. Higher dispersions were obtained using a lower heating rate (2 °C/min), an ammonia precursor, and a flowing gas stream (as opposed to static). Monitoring the emissions during calcination with time resolved mass spectrometry indicated that decomposition of the precursors could be achieved in helium and that subsequent treatment in oxygen was not required. Differential thermal analysis indicated that larger heat flows resulted at the higher heating rate (10 °C/min) and with the pyridine precursor, compared to the ammonia precursor. The larger heat flows may have caused more sintering and, thus, a lower dispersion. Toluene hydrogenation was used as a model reaction to demonstrate that the catalysts with higher dispersions had higher activities and better catalyst stability.

Graphical abstractThe effects of precursor and calcination procedure on the dispersion of 1.5 wt% alumina-supported Pt catalysts have been investigated. The prepared catalysts were characterized using X-ray diffraction, chemisorption, physisorption, and electron microscopy. Higher dispersions (up to 100%) were obtained with lower heating rates (2 °C/min), and an ammonia precursor. The decomposition of the precursors could be achieved with helium alone. Figure optionsDownload full-size imageDownload as PowerPoint slide