Catalytic ability on 12 kinds of carbide powders was investigated at room temperature using NOx gas degradation. They are largely classified into two groups, depending on whether the reaction involves a nitrogen gas in air or not. The carbon dangling bonds largely contribute to the reaction, while the accompanied metal atoms play an important role for adsorbing/dissociating nitrogen gas. Mechanical milling or annealing, as long as without agglomeration, is an effective method for activating powder catalysis, producing new surfaces with plenty catalytic sites. A new concept of catalysis is presented, based on the Schottky barrier-like model, where the charge imbalance is produced at the interface between the non-uniform thin oxide and the carbide.