Overview:

Research conducted at the Tufts Nano-CEL aims at applying principles of heterogeneous catalysis to the solution of problems in the production of clean energy.

A major research effort is in the area of catalytic hydrogen production reactions; e.g. fuel conversion to synthesis gas; steam reforming of hydrocarbons and alcohols; and the water-gas shift reaction. Effective catalysts for these reactions are highly dispersed metals (Au, Pt, Pd, Cu) on certain oxide supports. We investigate the catalyst structure-activity relationships in these systems by following specific metal structures (atoms, clusters, particles) and their activity and stability on selected oxides; and by evaluating the potential shape and crystal plane effect of oxides through careful preparation of the latter at the nanoscale according to novel synthesis techniques.

An important reaction in all fuel conversions is the water-gas shift reaction used to upgrade hydrogen gas streams. We have recently demonstrated that the active sites for this reaction reside on metal atoms embedded in the oxide surface. In the case of the Au-CeO_x catalyst system, the oxide structure and its defects control the dispersion of gold, and hence the final activity. To study these atomic-scale interactions, controlled synthesis techniques are used, as well as advanced characterization techniques to follow the structural evolution of the catalyst in situ as a function of the reaction conditions.

In the area of catalytic deNO_x of exhaust gas streams, we have found that atomically dispersed silver in alumina, Ag-O-Al, catalyzes the selective reduction of NO_x to nitrogen using methane as the reducing species. This reaction is important in the removal of NO_x pollutants from gas engines. We have recently demonstrated that the presence of SO₂ in the gas is necessary to keep the silver dispersed in the alumina matrix and avoid catalyst deactivation due to silver particle growth. Thus, this type catalyst may be a good choice for the removal of NO_x from hot flue gas streams exiting boilers and other heavy-fuel combustors emitting both sulfur dioxide and nitrogen oxides.

Mixed oxide/sulfide sorbent materials based on rare earths have been developed in recent work conducted in our lab for the high-temperature, regenerative desulfurization of fuel gas streams. We have identified a novel scheme of cyclic surface adsorption/desorption of hydrogen sulfide, which renders these sorbents regenerable at temperatures as high as 800^o C. The new technology is equally applicable to small-scale diesel fuel reformers combined with fuel cell systems, and to large-scale coal gasifiers to efficiently remove hydrogen sulfide from the hot fuel gas stream at the gasifier exit.