Ni nanoparticles (Ni(1) and Ni(2)) and Ni loaded SiMCM-41 (15Ni/SiMCM-41) were prepared and characterized with XRD, TEM, N 2 adsorption, CO chemisorption, and H 2 -TPR. The Ni specific surface area followed the order of 15Ni/SiMCM-41 > Ni(1) >> Ni(2), whereas the Ni particle size exhibited the opposite trend. These catalysts were utilized for vapour phase hydrogenation of cinnamaldehyde at 1 atm and 200°C in a fixed-bed, down flow reactor. The main products include hydrocinnamaldehyde, styrene, ethylbenzene, and 2-phenyl-1-propanol. The catalytic activity decreased in the same order as that of Ni specific surface areas. The SiMCM-41 support possessed very large surface area, leading to enhanced dispersion and specific surface area of Ni nanoparticles. As a result, the 15Ni/SiMCM-41 catalyst exhibited the highest activity. Based on the investigation of reaction pathways, it is important to emphasize that both hydrogenation and hydroelimination of formaldehyde (hydrodeformylation) occur in the vapour phase reaction.Keywords: Hydrogenation; Hydrodeformylation; Ni nanoparticles; Ni/SiMCM-41;Cinnamaldehyde. INTRODUCTIONThe Ni metal and Ni containing materials as hydrogenation catalysts have drawn much attention in both academic research and industrial application due to their chemical properties and low costs. Metal nanoparticles exhibit special properties of surface area, crystal size and shape, electron density, and ionization energies. Consequently, these materials exhibit better catalytic results in many reactions.