Abstract
In this present work, we studied the effects of preparation methods and Ni/Pd ratios on the catalytic activity of a Ni-promoted Pd/C catalyst for the formic acid dehydrogenation (FAD) reaction. Two catalysts prepared by co-impregnation and sequential impregnation methods showed completely different Pd states and catalytic activities. As the sequentially impregnated catalyst showed better activity than the co-impregnated catalyst, the sequentially impregnated catalyst was investigated further to optimize the ratio of Ni/Pd. The highest catalytic activity for the FAD reaction was obtained over the seq-impregnated catalyst having a 1 : 1.3 molar ratio of Pd : Ni. The results of X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed that small particle size is one factor improving the catalytic activity, while those of X-ray photoelectron spectroscopy (XPS) and X-ray adsorption near edge structure (XANES) indicate that the electronic modification of Pd to a positively charged ion is another factor. Thus, it can be concluded that the enhanced catalytic activity of the Ni-promoted Pd/C catalyst is attributed to the role of pre-impregnated Ni in facilitating the activity of Pd by constraining the particle growth and withdrawing an electron from Pd.