Iron-Catalyzed Selective Hydrogenation of Stearic Acid to Stearyl Alcohol

The utilization of sustainable resources such as biomass to produce fuels and chemicals has recently attracted significant attention due to the depletion of fossil reserves, increasing energy demand, and growing environmental concerns. Long-chain fatty acids, which are major constituents of plant oil, are important feedstock for biorefinery. Besides producing well-known biodiesels, the hydrogenation of fatty acids to fatty alcohols has recently drawn significant attention due to the versatility and growing market value of fatty alcohols. An example of heterogenous iron-catalyzed selective hydrogenation of stearic acid to stearyl alcohol is reported. Comparing with other reported non-noble metal centers, such as Co and Ni, Fe is 3000 similar to 30000 times more abundant and 20 similar to 150 times cheaper, thus making our method more economic and attractive. The iron catalyst was prepared by simultaneous pyrolysis of iron precursor [Fe(acac)(3)] and nitrogen-doped carbon precursor (melamine) onto alumina, bearing Fe3C active phase and nitrogen-doped carbon-alumina hybrid support. The optimization of preparation parameter showed that the optimal pyrolysis temperature is 900 degrees C, while the best mass fraction of iron is 20%. The replacement of Fe(acac) 3 with Fe(NO3)(3) led to inferior catalytic performance, which was due to undesired redox reaction between NO3- and melamine during pyrolysis that hampered the reaction between Fe and melamine to form Fe3C active phase. Instead, hercynite phase became the predominant phase. The exploration of reaction parameter showed that the optimal reaction temperature is 320 degrees C and the best H2 pressure is 4 MPa. The time course for stearic acid conversion shows that stearic acid was rapidly converted into stearyl alcohol with yield of 88.6% within 0.5 h, and then gradually converted into octadecane with yield of 90% at 4 h. The unsatisfactory stability of the iron catalyst is probably due to the decomposition of Fe3C active phase to metallic Fe phase during recycling tests.