Abstract
A series of monometallic platinum and bimetallic platinum–rhenium catalysts supported on mesoporous carbon Sibunit, which is a type of mesoporous, microcrystalline carbon, were investigated for hydrodeoxygenation (HDO) of isoeugenol (IE) at 200–300 °C and 30 bar of H2, using dodecane as a solvent. Catalytic activity was tested in a batch reactor to screen the catalysts and, for comparison, also in the continuous mode. For batch experiments, complete conversion, and a high yield of the desired product, propylcyclohexane (PCH), were obtained for all bimetallic PtRe/Sibunit in 240 min, with the highest yield of PCH when Pt:Re ratio was 1:1 or 1:3. The results for Pt–Re (1:1) were reproducible, in terms of catalytic activity and reusability of catalysts, which showed no deactivation. Monometallic Pt catalysts displayed low activity. Continuous experiments were performed with PtRe(1:1)/Sibunit at 30 bar H2, 0.5 mL/min of the liquid flow, and temperatures between 75 °C and 200 °C. The distribution of products showed deoxygenation at higher temperatures, while at lower temperatures, mainly oxygenated products were formed. XPS results confirmed the presence of ReOx species, where an increase in the platinum loading resulted in a decrease in the fraction of ReOx species and subsequently lower PCH yield.
Highlights
Fossil-derived fuels still provide most of the energy used worldwide, with its consumption still increasing yearly.[1]
The obtained bio-oil is rich in oxygenated compounds, making it unsuitable as a fuel, because of, for example, high viscosity, a low heating value, high acidity, and chemical instability.[5]
Sibunit, which is a type of mesoporous, microcrystalline carbon, is considered as an attractive material, because of its high mechanical strength,[27] reasonably large surface area, high purity, and chemical stability,[28] combining the properties of graphite and activated carbon
Summary
Fossil-derived fuels still provide most of the energy used worldwide, with its consumption still increasing yearly.[1]. The same catalyst was tested at 300 °C (Table 5, entry 2), resulting in the highest PCH Y (32%); the mass balance in the liquid phase at 4 h for reaction time was the lowest (32%), indicating that most products were distributed either in the gas phase, due to cracking, or as higher-molecular-weight polymers; neither of which was quantified. Bimetallic catalysts Pt−Re supported on Sibunit showed almost complete DH X (>98%) and a high PCH Y (>66%) (entries 6−8, Figure 10) Comparison of these results with monometallic Pt/Sibunit indicates that addition of Re had a noticeable effect on HDO activity, even if the slurry pH was not too acidic (Table 2). In a previous work[13] bimetallic PtRe/Al2O3 catalysts tested for HDO of isoeugenol under the same reaction conditions showed a lower PCH Y (54%) at 240 min These results suggest that the choice of support plays a very important role. Consistent with the literature results, the activation energy (Ea) for hydrogenation of the aromatic ring is lower than the Ea value for deoxygenation.[47]
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