New Catalyst Supports
There are a number of interesting attempts in recent years to improve the CO conversion rate as well as ethanol selectivity by changing the catalyst support from traditional supports like silica or alumina. Some of these new supports are discussed in the following section.
Graphitic mesoporous carbon (GMC) as a support for Rh catalysts
Graphitic mesoporous carbon (GMC) prepared through high temperature graphitization of soft-templated amorphous mesoporous carbon (AMC) was used as the support for Mn, Li, and Fe triple-promoted Rh catalysts in Song-Hai Chai’s work at Oak Ridge National Laboratory, USA [41]. The use of GMC results in C2H5OH selectivity and formation rate comparable to nonporous SiO2 support along with a significant inhibition on the formation of undesired CH4 and light hydrocarbons at the expense of appreciable amounts of CO2 produced. The better catalytic performance of promoted-Rh/GMC than those supported on other carbon allo — tropes (AMC and non-porous graphitic carbon black) seems to be associated with the specific graphitic structure and mesoporosity of GMC. The surface modification of GMC by wet oxidation leads to considerable increases in C2H5OH selectivity and formation rate. Furthermore, Song-Hai Chai’s group reported that, modified GMC as a support showed substantially greater selectivity for C2H5OH than the SiO2 support.
Ordered mesoporous carbon (OMC) as a support for Rh catalysts
Another example of this new generation of catalysts is reported in a 2012 publication by Song et al. [32] where an ordered mesoporous carbons (OMCs) containing highly dispersed iron and manganese bimetal particles have been synthesized by an organic-organic selfassembly method. The characterization results showed that the ordered mesostructure of carbons still remained after the incorporation of bimetal particles into the carbon matrix. These materials were used as supports of Rh based catalysts for ethanol synthesis from CO hydrogenation reaction. The catalysts supported on the metal modified OMC exhibited much better activity and selectivity than that supported on the OMC without modified metal particles and conventional catalysts supported on silica. A comparison of some ethanol selectivities of RhMnFe/OMC catalysts prepared with different particle sizes are shown in Table 13.5 [32].