Study On Catalytic Oxidation Of Low-Concentration Methane To Methanol Using Cu/MoO₃

For the purpose of protecting the environment,it is important to exploit lowcarbon fossil energy sources such as natural gas and coalbed methane,which are mainly composed of methane.However,during the extraction,transportation and utilization of these resources,large amounts of low-concentration methane also produce.If lowconcentration methane is not converted efficiently,it will not only cause energy waste,but also exacerbate the greenhouse effect.Methanol is an important basic raw material,which is widely used in many fields of industrial production.Therefore,the continuous oxidation of low-concentration methane to methanol in the gas phase system has both high environmental value and considerable economic value.The key to the continuous oxidation of low-concentration methane to methanol in the gas phase is the development of high-performance catalysts.In an effort to realize the continuous oxidation of low-concentration methane to methanol in the gas phase,Cu/MoO₃ catalyst with ordinary morphology was first prepared by impregnation method,and its catalytic performance was studied in detail.The results showed that the catalyst activity was the best under the conditions of copper loading of 2 wt.%,reaction temperature of 600 ℃,CH₄:O₂:H₂O=5:1.4:10.At this time,the methanol yield reached 47.2 μmol/（g·h）.Due to the limited number of active sites in the catalyst without specific morphology,the use of rod-like morphology could increase the specific surface area of the catalyst well,thereby helping the supported metal to better disperse and formed more active sites.Therefore,so as to further strengthen the catalytic ability,the rod-shaped MoO₃ carrier was synthesized by hydrothermal method.Then,the Cu/MoO₃-R catalyst was prepared by impregnation method.Under the same reaction conditions,the yield of methanol reached 54.5μmol/（g·h）,which was 7.3 μmol（g·h）higher than the former.The physicochemical properties of Cu/MoO₃ and Cu/MoO₃-R catalysts were studied by BET,XRD,TEM,SEM,H₂-TPR and other characterization techniques.The results showed that the Cu elements loaded on the MoO₃ support were uniformly distributed,and they could also interact with the carrier to form a new species CuMoO₄.IR,Raman,XPS and other spectroscopic techniques were further used to analyze the active species on the catalyst surface.CuMoO₄ was observed as the active site in the partial oxidation of methane to methanol,and the reaction path was as follows:（Ⅰ）methane was adsorbed and activated on CuMoO₄ to form methyl or methoxy groups,（Ⅱ）combined hydroxyl groups in water to form CH₃OH or CH₃OOH and desorption,（Ⅲ）oxygen underwent a reactivation process to regenerate catalyst activity.The characterization analysis was performed on the rod-shaped Cu/MoO₃-R catalyst.The consequences showed that compared with Cu/MoO₃ catalysts without specific morphology,it had three advantages:（1）the specific surface area was larger,which could help the reaction gas to contact the catalyst active site more fully;（2）the number of active sites was higher,which could help increase the rate of methane activation;（3）the number of surface oxygen vacancies increased,which could help adsorb and activate more reaction gases.