A key to progress: Identification of the state of catalysts during the catalytic reaction

We stress the importance of identifying the state in which catalysts are during the catalytic reaction. Catalysts as prepared do not correspond to the real working catalyst. Several examples will be recalled, and a new one (Mo-Te-O catalyst) will be mentioned. In a more detailed way, it will be shown that the working state of MoO₃ is Mo_xO_3x-2 with 8 ≤x≤18. The pitfalls encountered when focusing on catalysts as prepared (as opposed to catalysts “as they work”) is illustrated in the case of mixed Sb_xMo_yO_z oxides which decompose spontaneously during the reaction.