(560jg) Effect of Pd Precursors on Pd/TiO2 Catalysts Prepared by Different Methods and Their Catalytic Activity in Hydrogenation of Maleic Acid

Kim, Y. E., Korea Institute of Industrial technology
Byun, M. Y., Korea Institute of Industrial technology
Baek, J. H., Korea Institute of Industrial technology
Lee, K. Y., Korea University
Lee, M. S., Korea Institute of Industrial Technology
The size, shape, and distribution of metal clusters on TiO2 with strong metal-support interaction are generally controlled by the preparation methods, the nature of palladium precursors, pH values, etc.1,2 Herein, a series of 5 wt% Pd/TiO2 catalysts were prepared by varying two parameters; the types of palladium precursors and preparation methods. The catalytic performances were evaluated via hydrogenation of maleic acid (MA). The reaction was carried out under temperature=90 ℃, pressure of H2=3 bar, reaction time=60 min, and stirring rate=700 rpm. We prepared the Pd/TiO2 catalysts using four different precursors such as H2PdCl4 (H), K2PdCl4 (K), Na2PdCl4 (N), and Pd(NH4)Cl2∙H2O (PA) by different methods. We also investigated the effect of preparation methods (i.e. chemical reduction (CR), incipient wetness impregnation (IWI), and deposition-precipitation (DP)) on the Pd particles of the Pd/TiO2 catalysts. The prepared catalysts were denoted as follows: Pd/TiO2_A_B (A: Pd precursor, B: preparation method). The XRD, FT-IR, N2 physisorption, CO chemisorption, UV-vis spectroscopy, and XPS were employed to characterize the physicochemical properties of prepared catalysts. The CO chemisorption results showed that Pd/TiO2_K_DP had the highest Pd dispersion of 12.4%. K2PdCl4 (K) in the aqueous solution formed rapidly [Pd(OH)2]n, which could be uniformly precipitated the hydroxyl groups on TiO2 support.3 However, Pd/TiO2_PA_CR had the lowest Pd dispersion due to the self-reduction and agglomeration of Pd by interaction with the NH3 ligands, causing lower Pd dispersion.4 From the XPS results, Pd/Ti atomic ratio of Pd/TiO2_K_DP was the highest value of 0.079, while Pd/Ti atomic ratio of Pd/TiO2_PA_CR was lower than 1.97 times. It was found to be in accordance with the CO chemisorption results. The catalytic activities were evaluated via MA hydrogenation over prepared Pd/TiO2 catalysts. The MA conversion of almost 40% was achieved over Pd/TiO2_K_CR. Although Pd/TiO2_K_CR had similar Pd dispersion to Pd/TiO2_K_DP, the maleic acid conversion was different. From above XPS results, we suggested that the Pd2+/Pd0 ratio influenced the catalytic activity of maleic acid hydrogenation.5

Keywords: Hydrogenation, Maleic acid, Palladium catalyst, Pd/TiO2


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