Preparation And Catalytic Properties Of Supported Cobalt Silicide By Metal Organic Chemical Vapor Deposition

Transition metal silicides are important in semiconductor materials because of their high melting point, good electrical conductivity, high chemical inertness and thermal stability. Unfortunately, preparation methods for silicides inherited from the microelectronic industry result in low surface area. The controlled synthesis of well-dispersed metal silicides still remains an important challenge for catalytic applications.Here, we firstly reported metal organic chemical vapor deposition (MOCVD) of Co(SiCl3)(CO)4 as a single source precursor to highly dispersed CoSi nanoparticles on SiO2, SBA-15, CNTs and Al2O3 support, respectively. The catalysts were characterized by X-ray diffraction (XRD), N2-physorption, transmission electron microscopy (TEM), H2 temperature programmed reduction (H2-TPR) and H2 temperature programmed desorption (H2-TPD). The catalytic hydrogenation of naphthalene was investigated on supported cobalt silicides. Further in situ diffuse reflectance infrared Fourier transform spectroscopy(in-situ FT-IR) was applied to study the mechanism of adsorption and decomposition of the Co(SiCl3)(CO)4 precursor on supports. These results showed that:1. The organometallic precursor Co(SiCl3)(CO)4 was synthesized from Co2(CO)8 and SiHCl3 following a modified procedure, as confirmed by IR, NMR and C content.2. CoSi particles on silica support, synthesized by metal organic chemical vapor deposition (MOCVD) of Co(SiCl3)(CO)4 as a precursor at atmospheric pressure and moderate temperature in a fluidized bed reactor, show high catalytic activity and selectivity in naphthalene hydrogenation. Uniform nanostructured CoSi particles with a size of about 2-3 nm were evenly dispersed on the silica. The 13.5% CoSi/SiO2 catalyst showed a higher conversion and higher selectivity to tetralin in the naphthalene hydrogenation superior to those of 7.0% and 17.1% CoSi/SiO2 catalysts, which may be due to the size effect and the strong interaction of CoSi and support.3. Cobalt silicide nanoparticles in mesoporous silica SBA-15 were successfully prepared by metal-organic chemical vapor deposition of a single-source precursor. The results showed that the CoSi nanoparticles with a size of about 2-4 nm almost exclusively stayed inside the channels of the host SBA-15. The selectivity to tetralin over the 8.3% CoSi/SBA-15 catalyst showed that naphthalene converted to tetralin with a low conversion of naphthalene and a selectivity of 100%. The 16.1% CoSi/SBA-15 catalyst gave a conversion up to 87%, and the selectivity to tetralin decreased to the final selectivity of 35%.4. No particles were observed on CNTs support, however, the EDX showed the presence of small amount of Co and Si. While Al2O3 was used as support, the final product was COCl2/Al2O3.5. Argon treatment resulted in the formation of blue CoCl3SiO2, while the H2 treatment led to a stable sample CoSi/SiO2 by metal organic chemical vapor deposition in a fluidized bed reactor. The in-situ FT-IR results indicated that the reaction route was changed by inducing H2, which decreased the decomposition temperature. It is possible to synthesize supported cobalt silicides at lower temperature.