Methane conversion to synthesis gas over platinum supported on rare earth oxides.

摘要

The central theme of this research is to study methane conversion to synthesis gas focusing on the redox capabilities of cerium oxide.; Reaction of methane with platinum or ruthenium supported on Ce_1−x Zr_xO₂ (x = 0, 0.2, 0.5) in the absence of gaseous oxygen was studied in a packed-bed reactor at 550–700°C. The oxidation of methane utilized lattice oxygen of the support, which was restored by reacting with oxygen in a separate step. Thus, by using the redox property of cerium oxide, methane oxidation can be carried out by air without diluting the product with nitrogen. Addition of ZrO₂ into CeO₂ increased the reducibility of the oxide and the rate of methane oxidation but decreased the selectivity to CO and H₂. The rate of oxidation was initially fast but slowed down as the support progressively reduced. However, the selectivity increased with the reduction of the support and sharply rose to over 90% as the support attained 10%, 40%, and 65% degree of reduction for the oxide compositions x = 0, 0.2, and 0.5, respectively.; Methane partial oxidation to synthesis gas over 0.5wt% Pt/Al₂O ₃ and 0.5wt% Pt/CeO₂ catalysts was studied in a packed-bed reactor. At temperatures up to 650°C, the Pt/CeO₂ catalyst gave higher conversion and higher selectivity but the activity and selectivity became comparable to those of Pt/Al₂O₃ above 700°C. The Pt/CeO₂ catalyst also maintained high conversion and high selectivity when the CH₄:O₂ feed ratio varied from 1.7 to 2.3 while the Pt/Al₂O₃ catalyst had considerably lower selectivity under methane-rich conditions. The effect of reducibility of support on the catalytic activity was discussed.; A multireactor system for parallel testing of heterogeneous catalysts was developed. The reactor system was composed of nine tubular microreactors housed in a single wider tube and used a multiposition, valve to conduct the reaction products sequentially from each microreactor to a mass spectrometer for analysis. The catalyst samples were prepared in the form of thin films coated on quartz rods for convenience of preparation and loading samples in the reactors. The system was tested with the reaction of methane reforming with carbon dioxide over Pt/Ce_1−xGd_xO_2–0.5x and Pt/Ce_1−xSm_xO_2–0.5x at 650°C and 700°C.