Effect Of Plasma Treatment On The Catalysts For Methane Conversion

With the depleting of oil resource in the world, the utilization of natural gas (main component is methane) resources to useful chemicals has becoming important. From the economic consideration, it is more promising to use methane for syntheses of liquid fuels and oxygenated hydrocarbons via synthesis gas (H₂ and CO). There are three approaches to produce synthesis gas from methane, namely, reforming with H₂O (steam reforming), with CO₂ (CO₂ reforming), and partial oxidation. Steam reforming is currently carried out in the industry with some drawbacks, for example, intense energy input. Compared to steam reforming, CO₂ reforming and partial oxidation have some advantages, for example, utilization of greenhouses gases, lower energy input and higher space velocity for partial oxidation. Therefore, it is of great importance for the studies of CO₂ reforming and partial oxidation.The Ni/Al₂O₃ catalyst prepared using plasma treatment followed by calcination method shows excellent stability and superior reactivity for CH₄/CO₂ reforming, compared with the non-plasma treated sample. The activity did not decline during 50 h time on stream at 750 ?C. Temperature programmed oxidation results show that the amount of carbon formed over the non-plasma treated sample during CH₄/CO₂ reforming at 750 ?C for 5 h was 5.1 times larger than that for the plasma treated sample. The TEM observations do not reveal obvious filamentous carbon or encapsulating carbon for the plasma treated sample even after 50 h time on stream. Whereas these carbon species are clearly observed for the non-plasma treated sample after 10 h time on stream. These results indicates that the greatly inhibition of filamentous carbon and encapsulating carbon formation over the plasma treated sample. Various characterizations illustrate the smaller particle size of Ni, the stronger interactions between the Ni and alumna support, and the flatter morphology of Ni particle result in the superior anti carbon property of plasma treated sample.CO adsorbed diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy is a powerful way to study the structure of supported catalysts. A band centered at 1887 cm-1, which can be assigned to CO bridged bonded to three nickel atoms, is observed for the plasma treated Ni/Al₂O₃ sample. However, it is absent for the non-plasma treated sample. This result suggests that the nickel particle of the non-plasma treated sample is more rough, containing more defect sites; whereas, it is more flat, containing more close packed planes for the plasma treated sample. The Pt/ZrO₂ catalyst prepared using the plasma treatment and calcination method shows higher reactivity for the CH₄/CO₂ reforming with regard to the sample without plasma treatment. We tentatively ascribe the result to higher exposed Pt concentration after high temperature reduction and stronger Pt-ZrO₂ interactions for the plasma treated sample.Various approaches were used to confirm the validation of Ar glow discharge plasma reduction of supported Pt catalysts. And the plasma reduced supported Pt catalysts show comparable reactivity during partial oxidation of methane.The Pt/ZrO₂ catalyst prepared using the plasma treatment and calcination method shows higher stability for the partial oxidation of methane with respect to the sample without plasma treatment. The deactivation of the catalyst is not due to coke formation but Pt sintering in the presence of O2. CO adsorbed DRIFT study shows that the plasma treated sample is more resistance to sintering at higher temperature in the presence of O2.