A Study On The Catalytic Hydrogenation Of α-pinene

China is a country that produces large amount of turpentine, which contains abundant a-pinene. a-pinene can be used to produce pinane through the catalytic hydrogenation. Pinane has two isomers:cis-and trans-isomers, in which the cis-pinane is more active than trans-pinane for the further transformations to other useful products. Thus, it is important to produce more cis-pinane in industrial applications. Cis-pinane is a very important intermediate in terpene industry, especially for linalool and dihydromyrcene synthesis. So it is of great significance to prepare cis-pinane by catalytic hydrogenation of a-pinene.Supported nickel catalysts are important for various hydrogenation reactions. In this work, the catalytic properties of supported Ni and Ni-Cu catalysts for the hydrogenation of a-pinene were studied by using different phyico-chemical techniques combined with catalytic micro-reactor tests. The effects of ZrO2 promoter on the catalytic properties of supported Ni catalysts were studied as well. In this work, nickel catalysts with different supports and different loadings were prepared by the co-precipitation method. The surface structures and properties of the catalysts were characterized, and correlated to the catalytic activity and selectivity for the hydrogenation of a-pinene. The main results obtained in this work are summarized below:(1) In the fixed-bed reactor, the suitable conditions for the hydrogenation of a-pinene were found to be:P=2 MPa, T=343 K, space velocity= 2 h-1, and molar ratio of H2/α-pinene= 3:1. Ni/Al2O3, Ni/ZrO2, and Ni/MgO catalysts containing about 60 wt% of nickel were prepared by the co-precipitation method. They had the high nickel loading, reducibility and metal dispersion, so that they exhibited the high activity and cis-selectivity for the hydrogenation of a-pinene. Under these suitable conditions, the catalytic hydrogenation activity was in the following order:60%Ni/Al2O3> 60%Ni/MgO> 60%Ni/ZrO2.(2) The Ni/Al2O3 catalysts containing 30%,60%,80% and 90% nickel were prepared by the co-precipitation method. Under the optimized conditions, the catalytic hydrogenation activity of the catalysts followed the order:60%Ni/Al2O3> 30%Ni/Al2O3> 80%Ni/Al2O3> 90%Ni/Al2O3. Low nickel loadings seemed to favor the cis-selectivity, while the higher nickel loading seemed to reduce the cis-selectivity. All these catalysts had the mesoporous structure with the high reducibility of supported nickel. With the increase of nickel loading, the BET surface area and pore volume dropped significantly. Specifically, when the nickel loading increased from 60% to 90%, the dispersion of nickel was decreased significantly, leading to the significantly decreased hydrogenation activity.(3) The 60%Ni/ZrO2-Al2O3 catalysts containing 2%,4%,8%,16% and 32% ZrO2 were prepared by the co-precipitation method. With the increase of ZrO2 loading, the BET surface area and the dispersion of nickel decreased significantly, leading to the decreased catalytic hydrogenation activity. High ZrO2 loading (>16%) seemed to have low hydrogenation activity and low cis-selectivity. When the loading of ZrO2 was low, the activity of the catalysts followed the order:60%Ni/Al2O3-2%ZrO2> 60%Ni/Al2O3-4%ZrO2> 60%Ni/Al2O3-8%ZrO2. The addition of some ZrO2 favored the cis-selectivity. For example, the 60%Ni/Al2O3 and 60%Ni/Al2O3-4%ZrO2 had the cis-selectivity of 92% to 96%, respectively. Microcalorimetric adsorption of NH3 and CO2 was used to probe the surface acid/base properties of catalysts. The addition of ZrO2 increased the initial heat of CO2 adsorption, indicating the increased surface base of Ni-ZrO2/Al2O3 as compared to the Ni/Al2O3. Thus, the strong surface acidity did not seem to favor cis-selectivity for the hydrogenation of a-pinene. The 60%Ni/Al2O3-4%ZrO2 was found to be the best by considering the activity and cis-selectivity for the hydrogenation of a-pinene.(4) The Ni-Cu/4%ZrO2-Al2O3 catalysts containing a different proportion of Ni-Cu (Ni: Cu=0,1/11,0.2,0.5,2,5 and 11) were prepared by the co-precipitation method. All the catalysts had the mesoporous structure. The pure copper catalyst showed the sharp XRD peaks indicating the larger particle sizes of supported copper and thus it had the low activity for the hydrogenation of a-pinene. In contrast, the Ni-Cu catalysts exhibited the wider XRD peaks, indicating that the addition of Ni improved the dispersion of Cu. The nickel catalysts were much more active than the copper catalysts for the hydrogenation of pinene. The activities of the Ni-Cu alloy catalysts dropped significantly with the increase of copper loading. However, the addition of a small amount of copper in the nickel catalysts improved the activity and cis-selectivity. As compared to the 60%Ni/ZrO2-Al2O3, the 50%Ni-10%Cu/ZrO2-Al2O3 showed the better catalytic stability. However, its activity still dropped rapidly after 60 hours on-stream. Thus, the addition of Cu did not improve much the catalytic stability of Ni for the hydrogenation of α-pinene. The problem of deactivation of catalysts remained for the hydrogenation of α-pinene in α fix-bed reactor.