Strontium as an efficient promoter for supported palladium hydrogenation catalysts

The effect of strontium promotion is studied for a series of supported palladium catalysts such as Pd/zeolite-β, Pd/Al2O3, Pd/SiO2, Pd/hydrotalcite and Pd/MgO. Strontium is found to be an effective promoter for enhancing the metal area, percentage dispersion of the metal and therefore the hydrogenation activity of the different supported palladium catalysts with varying acid/base properties. The effect of addition of Sr and Pd onto the support by simultaneous and sequential impregnation methods is studied besides the effect of Sr/Pd ratio. It is revealed that when sequential addition of Sr and Pd by impregnation is advantageous for alumina, silica, magnesia and hydrotalcite supported palladium catalysts, simultaneous impregnation of Sr and Pd is found to be more effective for zeolite-β supported catalyst. This may be attributed to the microporous nature of the zeolite support that could cause the migration of Sr to its micropores thereby making them non-available for the promotional effect if added first. Addition of strontium is also found to enhance the basicity of the supported palladium catalysts. TPR studies suggest a change in the metal environment upon Sr-promotion indicating an electronic effect responsible for the improvement in the hydrogen adsorption capacity and hydrogenation activity. The promotional effect of Sr on the supported palladium catalysts is explained to be both electronic and physical in nature.