An experimental investigation of natural gas catalysts using a bench-flow reactor

A computer-controlled bench-flow reactor was constructed and used to study the effects of feed stream composition, Pd/Rh loading and washcoat composition on the conversion efficiency of natural gas catalysts. Both fresh and thermally aged catalysts were evaluated using noncycled rich, noncycled lean and cycled stoichiometric feed streams. Results indicated that the cycled stoichiometric feed stream was the optimum feed stream for effective three-way removal of CH₄, NO_x, and CO for both the fresh and aged catalysts. In addition, the conversion of CH₄, NO_x and CO was found to be maximized with higher Pd/Rh loadings for both the fresh and aged catalysts. By adding ceria to the washcoat, the conversion efficiencies of NO_x and CO was enhanced for the fresh catalysts while the conversion of CH₄ was not affected. Thermal degradation was found to be a function of Pd/Rh loading on the catalyst, with higher loadings providing a higher degree of resistance to thermal degradation. On the other hand, aged catalysts containing ceria additives were found to degrade considerably which resulted in lower conversion efficiencies for CH₄, NO_x and CO as compared to the ceria-free aged catalysts. It is recommended that further investigations be conducted using dynamometer tests employing a dedicated NGV engine with the catalyst configurations used in this study. In addition, the natural gas catalysts should be evaluated with variable levels of ceria in order to find the level of ceria necessary for an effective oxygen storage capability while providing resistance to thermal degradation.