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 substrat es for microelectronics have clearly shown that it is possible to reach hig h-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 catalyst s 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 spec trometry of the precursor complexes as well as their thermal behavior are r eported (TGA, DSC, vapor pressure equations), introduction of hydrogen in t he 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) a re suitable precursors to produce pure thin films at these remarkably low t emperatures. Pt(hfa)(2) gave poor results since the deposits are contaminat ed 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 particle s of palladium and platinum on silica can be prepared under very mild tempe ratures (below 120 degrees C). TEM micrographies revealed a narrow size dis persion of the nanoparticles (average size 1-3 nm). EDX analyses did not sh ow any contamination of the deposits. A high supersaturation regime was ide ntified to be a crucial parameter in the fluidized bed-MOCVD method, allowi ng a good nucleation rate with regard to the growth rate. Catalysts prepare d by this method, and containing palladium and platinum on porous silica, w ere highly active for the dehydrogenation of cyclohexane.