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°C). The Ir-particle size was determined by XRD to be ~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, KA, and the modified surface rate constant, ksKH, were calculated to be 87 M^-1 and 5×10^-4 M min^-1 bar^-1 gcat ^-1, respectively.