The most effective metal catalyst for the selective oxidation of methane to methanol on metal surfaces is generally considered to be copper-exchanged zeolites, specifically Cu-SSZ-13 and Cu-MOR. These catalysts have shown promising results in terms of selectivity and activity.The reaction conditions for this process are also crucial for achieving high selectivity and conversion. Optimal reaction conditions include:1. Temperature: The reaction temperature should be maintained between 150-250C. Lower temperatures may result in low conversion rates, while higher temperatures can lead to over-oxidation and the formation of undesired byproducts.2. Pressure: Moderate pressures, typically around 1-10 bar, are preferred for this reaction. Higher pressures can improve the conversion of methane, but may also increase the formation of undesired byproducts.3. Oxygen source: The use of an oxygen source, such as molecular oxygen O2 or nitrogen oxides NOx , is necessary for the oxidation of methane to methanol. The choice of oxygen source can significantly impact the selectivity and conversion of the reaction.4. Gas composition: The ratio of methane to oxygen in the reaction mixture is important for achieving high selectivity and conversion. A stoichiometric ratio of methane to oxygen 1:1 is typically used, but the exact ratio may need to be optimized for specific catalysts and reaction conditions.5. Reaction time: The reaction time should be carefully controlled to prevent over-oxidation and the formation of undesired byproducts. Short reaction times on the order of seconds to minutes are typically preferred.In summary, the most effective metal catalyst for selective oxidation of methane to methanol on metal surfaces is copper-exchanged zeolites, and the optimal reaction conditions include moderate temperatures and pressures, an appropriate oxygen source, a balanced gas composition, and controlled reaction time.