Platinum and palladium films obtained by low-temperature MOCVD for the formation of small particles on divided supports as catalytic materials

CVD studies devoted to platinum and palladium deposition on planar substrates for microelectronics have clearly shown that it is possible to reach high-quality deposits at temperatures above 200 degrees C. Attempts to prepare pure metallic deposits at temperatures around 100 degrees C and even lower are of general interest, since a number of temperature-sensitive supports could be then exploited. An other attracting issue in the field of catalysts elaboration is presented here. Pt(hfa)(2), PtMe2(cod), Pd(Cp)(eta(3)-C3H5), and Pd(eta(3)-C3H5)(hfa) have been selected to produce by MOCVD platinum and palladium deposits on planar and on divided supports. The EI-mass spectrometry of the precursor complexes as well as their thermal behavior are reported (TGA, DSC, vapor pressure equations), introduction of hydrogen in the carrier gas results in a dramatic decrease of the deposition temperature (35-120 degrees C) of the complexes. XPS and electron microprobe analyses have shown that PtMe2(cod), Pd(Cp)(eta(3)-C3H5), and Pd(eta(3)-C3H5)(hfa) are suitable precursors to produce pure thin films at these remarkably low temperatures. Pt(hfa)(2) gave poor results since the deposits are contaminated with fluorine, oxygen, and principally carbon. Using the CVD method in a fluidized bed under reduced pressure conditions allowed the deposition of the metals on porous divided substrates. Highly dispersed metallic particles of palladium and platinum on silica can be prepared under very mild temperatures (below 120 degrees C). TEM micrographies revealed a narrow size dispersion of the nanoparticles (average size 1-3 nm). EDX analyses did not show any contamination of the deposits. A high supersaturation regime was identified to be a crucial parameter in the fluidized bed-MOCVD method, allowing a good nucleation rate with regard to the growth rate. Catalysts prepared by this method, and containing palladium and platinum on porous silica, were highly active for the dehydrogenation of cyclohexane.