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)(4)Cl-2, Pt(C5H5N)(4)Cl-2, Pt(CH3NH2)(4)Cl-2, or Pt(C4H9NH2)(4)Cl-2) and calcination procedure (heating rates of 2 degrees C/min or 10 degrees 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 H-2 chemisorption. The catalyst structures were characterized using X-ray diffraction, N-2 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 degrees 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 degrees 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. (c) 2006 Elsevier B.V. All rights reserved.