Liquid-Phase Hydrogenation of Cinnamaldehyde Over Ir Catalysts: A Kinetic Modeling Study

The liquid phase hydrogenation of cinnamaldehyde in toluene over alumina supported Ir catalysts was investigated under mild conditions (cinnamaldehyde concentration = 0.015 M - 0.060 M, hydrogen pressure = 3-7 bar and T = 55-95 degrees C). The Ir-particle size was determined by XRD to be similar to 6 nm with a dispersion of 28-35% and in good agreement with that determined by means of hydrogen chemisorption measurements. Under above reaction conditions, the order of reaction was experimentally found to be -0.5 with respect to cinnamaldehyde and 1 with respect to hydrogen. The apparent activation energy was practically zero. The kinetic data could be modeled based on the assumption that the Langmuir-Hinshelwood surface reaction between competitively adsorbed cinnamaldehyde and hydrogen is the rate determining step. The adsorption equilibrium constant of cinnamaldehyde, K-A, and the modified surface rate constant, k(s)K(H), were calculated to be 87 M-1 and 5x10(-4) M min(-1) bar(-1) g(cat)(-1), respectively.