Impact of the Oxygen Defects and the Hydrogen Concentration on the Surface of Tetragonal and Monoclinic ZrO2 on the Reduction Rates of Stearic Acid on Ni/ZrO2

• Published in: Chemistry : a European journal Vol. 21; no. 6; pp. 2423 - 2434
• Main Authors: Foraita, Sebastian, Fulton, John L., Chase, Zizwe A., Vjunov, Aleksei, Xu, Pinghong, Baráth, Eszter, Camaioni, Donald M., Zhao, Chen, Lercher, Johannes A.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 02.02.2015; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Subjects: Adsorption; Carboxylic acids; Catalysis; Chemistry; decarbonylation; EDX-TEM; Fatty acids; hydrodeoxygenation; Hydrogen - chemistry; Hydrogenation; Infrared spectroscopy; IR spectroscopy; isotopes; Kinetics; Nickel - chemistry; Oxidation-Reduction; Oxygen; Oxygen - chemistry; Physicochemical properties; Spectrometry, X-Ray Emission; Spectrophotometry, Infrared; Stearic Acids - chemistry; Temperature; XAFS; Zirconium - chemistry; hydrodeoxygenation; decarbonylation; EDX-TEM; IR spectroscopy; isotopes; XAFS
• ISSN: 0947-6539; 1521-3765; 1521-3765
• DOI: 10.1002/chem.201405312

The role of the specific physicochemical properties of ZrO2 phases on Ni/ZrO2 has been explored with respect to the reduction of stearic acid. Conversion on pure m‐ZrO2 is 1.3 times more active than on t‐ZrO2, whereas Ni/m‐ZrO2 is three times more active than Ni/t‐ZrO2. Although the hydrodeoxygenation of stearic acid can be catalyzed solely by Ni, the synergistic interaction between Ni and the ZrO2 support causes the variations in the reaction rates. Adsorption of the carboxylic acid group on an oxygen vacancy of ZrO2 and the ion of the α‐hydrogen atom with the elimination of the oxygen atom to produce a ketene is the key to enhance the overall rate. The hydrogenated intermediate 1‐octadecanol is in turn decarbonylated to heptadecane with identical rates on all catalysts. Decarbonylation of 1‐octadecanol is concluded to be limited by the competitive adsorption of reactants and intermediate. The substantially higher adsorption of propionic acid demonstrated by IR spectroscopy and the higher reactivity to O2 exchange reactions with the more active catalyst indicate that the higher concentration of active oxygen defects on m‐ZrO2 compared to t‐ZrO2 causes the higher activity of Ni/m‐ZrO2. Finding the best: Three different Ni/ZrO2 catalysts have been tested with regard to their efficiency in the hydrogenation reaction of stearic acid. The Ni/m‐ZrO2 catalyst was found to be the best one. A higher concentration of active oxygen defects present in this combination was identified to be responsible for the superiority of this catalyst over the other systems (see scheme).