The apparent activation energy ( app Ea) and reaction order are mainly used as indicators of the activity of heterogeneous catalysts. Both of them are affected by the coverage in the equation . Since the coverage is affected by the reaction conditions, app Ea and the reaction order are affected by the reaction conditions. In fact, for Fe-based catalysts with alkali metal additions, coverage and reaction order have been found to be temperature dependent . First-principles calculations of the energy on the catalyst surface for Ru-based catalysts have also shown that the coverage and the reaction order are affected by temperature . Therefore, understanding the effect of coverage on catalytic activity is very important for understanding elementary reactions on the catalyst surface and creating better catalysts.