Significance Statement
Fixed bed catalysts are widely used for large-scale chemicals production. Many such catalysts consist of metal (often a precious metal) particles spread over a support such as silica, alumina or carbon. How well a catalyst works depends upon how well distributed the metal particles are over the support, the amount of accessible surface area, how quickly reactants get transported to the surface of the catalyst and how quickly products get transported away from the catalyst surface, and how effectively heat is transported to and from the metal particles. Also critical is how long the catalyst functions before it needs to be replaced.
Hierarchically porous supports have networks of micrometer scale pores that provide efficient transport of reactants and products into and out of the catalyst, coupled to nanometer scale pores that provide large surface area. The micrometer scale pores are expected to make the catalyst more tolerant to deactivation by clogging. Carbon is a cheap and renewable material that has good chemical stability and provides good heat transfer. Nickel is an earth abundant metal that is considerably cheaper than precious metals such as palladium and platinum which often widely used in catalysis. By combining appropriate precursors of nickel and carbon in a single solution the synthesis is expected to be significantly cheaper than for existing processes for making carbon supported catalysts. It is also likely that the catalyst produced by this new process will have significantly different properties, as a number of processing steps that impact the final catalytic properties are avoided. Recent work on biomass conversions is confirming that the catalytic properties are different and advantageous for some processes.
Although the work reported is for synthesis of a nickel containing catalyst it is believed that the process will be a relatively general method that can readily be extended to other transition metal containing catalysts.
The work has been sufficiently promising that The University of Alabama has filed a preliminary United States patent on this class of materials.
The work potentially has broader impact in the area of monolithic microreactors. These are reactors are of considerable interest for fine chemicals production particularly pharmaceuticals where there the better quality control available from continuous processes has significant advantages. The synthesis reported can readily produce monoliths (i.e. single pieces) of 2-20 mm diameter and lengths to 20 cm.
Journal Reference
Materials Research Bulletin, Volume 73, January 2016, Pages 204-210.
Trupti V. Kotbagi, Yasemin Hakat, Martin G. Bakker
Department of Chemistry, The University of Alabama, Tuscaloosa, Al 35487-0336, United States
Abstract
Described is a novel, facile route for the synthesis of nickel supported on hierarchically porous carbon (Ni/HPC) using a one-pot co-gelation sol–gel method. Ni/HPC with varying nickel loadings (0.5, 1, 2.5 and 5 wt% Ni) were synthesized and the materials characterized by nitrogen physisorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) and Raman spectroscopies. The results show a three-dimensional network of disordered carbon with fine nickel nanoparticles of sizes ranging from 8 nm to 13 nm at 0.5 wt% Ni loading which gradually increased with increase in the Ni loading. The carbon structure was retained at the macropore level, but not at the mesoscale where the ordered mesopores were lost on nickel addition. The nickel nanoparticles were observed to grow on the surface of the ligaments. This may make them particularly suitable for low pressure Ni-catalyzed organic transformations e.g., hydrogenations, C–C coupling, C-heteroatom coupling, etc
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