Preparation of palladium catalysts using the strong electrostatic adsorption technique for stearic acid conversion via the deoxygenation process

• Main Authors: B. Kreatananchai, E. Somsook, T. Kiatsiriroat, K. Punyawudho
• Other Authors: Mahidol University
• Format: Article
• Published: 2022
• Subjects: Biochemistry, Genetics and Molecular Biology; Chemistry; Engineering; Materials Science; Physics and Astronomy
• Online Access: https://repository.li.mahidol.ac.th/handle/123456789/76089

The strong electrostatic adsorption (SEA) technique was used to prepare palladium catalysts on a graphene support to convert stearic acid to diesel-like hydrocarbon via a deoxygenation process. The pH shifts of graphene were determined, and the point of zero charge (PZC) was obtained at pH = 4.6. With a moderately low PZC, the cation Pd precursor (i.e., [Pd(NH3)4]2+—palladium tetraammine—PdTA) was preferred. In the adsorbed conditions, PdTA and the graphene surface attained the strongest electrostatic adsorption at pH = 12 and had the maximum metal surface density around 0.6 μmol/m2. The Pd loading of 5 wt% catalysts was controlled by the initial concentration of PdTA. The Pd particle size distribution was considerably uniform and had a diameter around 2–3 nm according to transmission electron microscopy (TEM). The ring pattern from electron diffraction (ED) and the spectra from X-ray diffraction (XRD) verified that the Pd metal had a face-centered cubic (fcc) crystal structure. The deoxygenation reaction was carried out and reached 99% conversion of stearic acid using 5 wt% Pd/graphene catalysts with mass of 0.6 g. The main product was straight chain hydrocarbon called heptadecane (C17H36), suggesting a decarboxylation pathway. Moreover, the diesel-like hydrocarbon (C16–C21) attained a maximum selectivity at 85.4%.