## 3 Results and Discussion
### Reaction Mechanism for Thermocatalytic Decomposition of DMMP
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Vibrational Mode**} & \multicolumn{6}{c}{**IR Frequencies (cm\({}^{-1}\))**} \\ \cline{2-7}  & **2 MCeO\({}_{2}\)np** & **12 MCeO\({}_{2}\)nr** & **12 MCeO\({}_{2}\)nc** & **Reference [53]** & **Reference [54]** & **Reference [56]** \\ \hline \(\
u\)(OH) & 3701 & / & 3709 & 3710 & 3724 & 3720 \\ \(\
u\)(OH) & 3659 & 3655 & / & 3660 & 3656/3651 & 3652 \\ \(\
u\)(OH) & / & 3554 & 3594 & 3600 & 3616 & / \\ \(\
u_{\mathrm{s}}\)(P\(-\)CH\({}_{3}\)) & 2930 & 2928 & 2914 & / & / & / \\ \(\
u_{\mathrm{s}}\)(O\(-\)CH\({}_{3}\)) & 2854 & 2874 & 2876 & / & / & / \\ \(\
u\)(Ce\(-\)O\(-\)CH\({}_{3}\)) & 2813 & 2813 & 2813 & / & / & / \\ \(\
u\)(Ce\(-\)H\({}_{3}\)) & 28(C\(-\)H) & 2716 & 2716 & / & / & 2721 & / \\ \(\
u_{\mathrm{a}}\)(OCO) \({}^{1}\) & 1615 & 1620 & / & 1599 & 1609 & / \\ \(\
u_{\mathrm{a}}\)(OCO) \({}^{2}\) & 1535 & / & / & 1553 & 1549 & 1552/1550 \\ \(\
u\)(CO\({}_{3}\)) \({}^{3}\)[57] & 1396 & / & / & 1354 & / & / \\ \(\delta\)(C\(-\)H) & 1365 & 1363 & / & 1371 & 1367 & 1375/1372 \\ \(\delta_{\mathrm{s}}\)(P\(-\)CH\({}_{3}\)) & / & 1318 & 1318 & / & / & / \\ \(\
u\)(CO\({}_{3}\)) \({}^{5}\)[57] & / & 1318 & 1318 & / & / & / \\ \(\
u\)(CO\({}_{3}\)) \({}^{5}\)[57] & / & / & 1236 & / & / & / \\ \(\
u\)(CO\({}_{3}\)) \({}^{4}\)[57] & 1294 & / & / & 1289/ & / & / \\ \(\
u\)(P\(-\)O) [32; 55] & 1262 & 1279 & 1272 & / & / & / \\ \(\
u_{\mathrm{a}}\)(P\(-\)O) [32; 55] & 1213 & 1208/ & 1130 & / & / & / \\ \(\
u_{\mathrm{s}}\)(P\(-\)O) [32; 55] & 1056 & 1169 & 1050 & / & / & / \\ \hline \hline \end{tabular}  
* \({}^{1}\), monodentate formate species; \({}^{2}\), bidentate (bdt) formate bound to two Ce\({}^{4+}\) atoms; \({}^{3}\), monodentate carbonate; \({}^{4}\), bidentate carbonate; \({}^{5}\). bridged carbonate.  
\end{table} 
Table 7: Assignments of IR frequencies in surface species. hydroxyl group (Scheme 1h) [56]. Moreover, CO\({}_{2}\) adsorption on surface oxygen could result in monodentate carbonate and bidentate carbonate (Scheme 1i) [57; 61]. When compared to the side reaction pathway of 2 MCeO\({}_{2}\)np (Scheme 1 II), the reactions of Scheme 1d-g on 12 MCeO\({}_{2}\)nr (Scheme 1 III) are the same as that on 2 MCeO\({}_{2}\)np. In addition, based on in situ DRIFTS analysis, the bridging carbonate may exist on 12 MCeO\({}_{2}\)nr, which is formed via the complete dehydrogenation of the surface methyl group (Scheme 1j) [60]. Based on in situ DRIFTS analysis, no formate is formed on the surface of 12 MCeO\({}_{2}\)nc, therefore, no reaction pathway of Scheme 1f occurred on 12 MCeO\({}_{2}\)nc (Scheme 1 IV); the other reaction pathways are the same as 12 MCeO\({}_{2}\)nr. According to the proposed reaction path, surface oxygen (surface lattice oxygen or adsorbed oxygen) participates in the oxidative decomposition of DMMP. It is well known that CeO\({}_{2}\) possesses an excellent oxygen storage and release capacity. In higher temperature reactions, the mechanism of CeO\({}_{2}\) is primarily the Mars-van Krevelen mechanism [62]. Thus, when the surface oxygen is consumed, the bulk oxygen and the external oxygen (such as oxygen, water molecules) will replenish the oxygen vacancy for the next catalytic DMMP decomposition cycle (Scheme 1k) [53]. The catalyst will eventually become completely deactivated when the byproducts fully cover the active sites on its surface.