Efficient aerosol assisted delivery of low-volatility precursor for CVD applications

An improved lab-scale process for coating of carrier particles by aerosol assisted chemical vapor deposition (CVD) is described and characterized to produce a highly dispersed, supported noble- metal catalysts. The process is based on a fluidized bed (FB) operated at atmospheric pressure and focusses on an efficient and lossless delivery of precursor vapor, including vapors of low-volatility precursors, to the bed. Precursor is aerosolized (at ambient temperature) applying a suitable solution and then delivered into the FB from above via a double-walled heated tube in which the aerosol is sublimated, the vapor is adsorbed on the carrier particles and then decomposed.
Degree of sublimation, delivery rates and usage efficiencies were investigated applying a tandem-DMA set-up with two precursor substances, namely Pd(TMHD)2 and MeCpPtMe3 dis- solved in butanone. At 150 °C and a residence time of about 2.5 s, precursor aerosol particles up to about 700 nm were found to sublimate to ≥ 99%. The degree of sublimation could have been increased further by extending the residence time in the sublimation zone. For higher volatility precursors, vaporization/sublimation can be assumed to be complete.
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Based on a mass balance of precursor amounts generated, delivered to the bed, and noble metal amounts recovered on the bed material it was found that the method of precursor delivery to the FB from above in combination with aerosol assisted precursor sublimation permits a quasi- lossless method of supplying and using precursor for coating.
The produced catalysts showed superior noble metal dispersion when compared with a commercial sample of same mass loading. The distribution of noble metal nanoparticles (in the range 1–2.2 nm) on an Al2O3 support was found to be very uniform.