There is tremendous global interest focused on renewable fuel sources for transportation. The Catalysis for Renewable Fuels Center is developing new catalysts for the production of hydrogen and alternative fuels from renewable sources for the transportation sector. These new catalysts are the next wellhead as the transportation sector moves to less dependence on imported oil and carbon fuel.
The Catalysis for Renewable Fuels Center was established at the University of South Carolina in 2005 through the SmartState South Carolina Centers of Economics Excellence program. Work associated with this Center has led to the creation of a startup company, Palmetto Fuel Cell Technologies. The Catalysis for Renewable Fuels Center also serves as a resource for recruiting activities in the Midlands of South Carolina for companies associated with renewable fuels, fuel cells and alternative energy sources.
The major research avenues of our group are the study of the preparation of solid catalysts. A typical example is the platinum or rhodium containing automobile catalytic converter used to eliminate carbon monoxide, nitric oxide and hydrocarbons from auto exhaust. Solid catalysts are usually composed of a metal or metal oxide deposited onto or supported on a high surface area, refractory oxide, which produces small, well anchored metal particles with a maximum amount of exposed metal surface.
Our current efforts involve the use and comparison of different methods for synthesis of a variety of catalysts especially using Strong Electrostatic Adsorption (SEA) in producing catalysts with high dispersion. The studies are also done to rigorously and systematically verify an underlying theory we have revived from the colloid science literature to predict how much metal will be adsorbed by the oxide for a full range of liquid conditions. We also investigate coupled methods for catalyst synthesis especially in the cases of bimetallic and bifunctional catalysts.
In a second vein of work, we look at a further step of catalyst preparation. After impregnation and drying, the catalyst is put through a series of heat and chemical treatments to activate the metal. We study how the shape and chemical structure of the deposited metal particles change as a function of pretreatment conditions. In some cases, the size and shape of particles can be controlled. For these studies we use various types of characterization techniques such as electron microscopy and x-ray diffraction.
The Catalysis for Renewable Fuels Center is directed by John Regalbuto, Professor of Chemical Engineering and Endowed Chair in Renewable Fuels. Dr. Regalbuto directs a team of research faculty, postdocs, visiting scholars and graduate students associated with the center.
Supported nanoparticles containing more than one metal have a variety of applications in sensing, catalysis, and biomedicine. Common synthesis techniques for this type of material often result in large, unalloyed nanoparticles that lack the interactions between the two metals that give the particles their desired characteristics. We demonstrate a relatively simple, effective, generalizable method to produce highly dispersed, well-alloyed bimetallic nanoparticles. Ten permutations of noble and base metals (platinum, palladium, copper, nickel, and cobalt) were synthesized with average particle sizes from 0.9 to 1.4 nanometers, with tight size distributions. High-resolution imaging and x-ray analysis confirmed the homogeneity of alloying in these ultrasmall nanoparticles. (Science, 2017, 358, 6369, 1427)
Graphene materials as catalyst supports have shown tremendous promise for improving catalytic activity. Pd nanoparticles supported by graphene defects have been shown to improve catalytic activity in Suzuki reactions, but understanding their formation and factors that affect their formation is still elusive. In order to gain a better understanding of this phenomenon, a new synthetic method was developed combining strong electrostatic adsorption method for directed ionic Pd precursor uptake with a new solventless microwave irradiation method to simultaneously form Pd nanoparticles and graphene defect sites. Catalytic activities an order of magnitude higher than commercial Pd-carbon catalysts were obtained using this new method with low microwave powers, short reaction times, under atmospheric conditions, and without the use of reducing agents or solvents. The systematic comparison of catalysts synthesized from four different graphene materials and two different Pd precursors revealed Pd-graphene defects form through three routes that are affected by the initial oxygen content of graphene support and choice of ionic Pd precursor. (Applied Catalysis A: General 2018, 550, 168)
To determine whether the method of “strong electrostatic adsorption” (SEA) can be extended to the preparation of carbon-supported Pt catalysts, a series of carbons of different type (activated, black, and graphitic) with different surface areas and points of zero charge (PZC) has been studied. Cationic Pt tetraammine, [(NH₃)₄Pt]²⁺, was adsorbed over low- and mid-PZC carbons in the high pH range, while anionic hexachloroplatinate (IV), [PtCl₆]²⁻, was adsorbed over high-PZC carbons in the low pH range. Adsorption equilibrium was determined by measuring pH and metal concentration in the impregnation solution before and after contacting with the carbon supports. Filtered, dried materials were reduced in hydrogen, and the Pt particle size was characterized by Z contrast imaging. Electrostatic adsorption occurs at short contact time (1h) for both Pt anions and cations. The adsorptive behavior of all carbons of like PZC is the essentially the same, independent of type and surface area. There are pH optima at which electrostatic adsorption is strongest; a sharp maximum occurs for anions in the low pH range at pH 2.9, while the high pH optimum for cations is pH 12. To attain the required final values, pH buffering by the surface, a phenomenon not sufficiently appreciated in the literature, has to be overcome. Particles synthesized by SEA are normally in the 1–2nm range and are as small as or smaller with narrower size distributions than by other methods, especially at high metal loadings. Results also reveal a longer time scale, reductive mechanism that occurs with Pt(IV) chlorides over carbon at low pH, which mitigates the need for precise pH control if the contact time is long, and might explain the small particle sizes obtained by dry impregnation with the [PtCl₆]²⁻ complex. This mechanism will be more fully explored in future work. (Journal of Catalysis 2011, 279, 48)