“…[28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] This also applies to Kc ompounds as promoters for oxidic catalysts. [12,19,[44][45][46][47][48][49][50][51] As stated above, the mechanistic role of Ki sn ot yet clear,and atremendous number of postulated mechanisms can be found in the literature. These mechanismsr ange from broad general statements to very specificp rinciples: * Kf acilitatesc ompounds with low melting points or eutectic mixtures, [14,[51][52][53] * Kacts as an electron donor with surface oxygen ast he electron acceptor (and subsequentf ormation of phenoxide species or gaseous K), [30,31,50,51] * Kd ecreases the stability of carbonates on the surface, which leads to lower decomposition temperatures of the carbonates, [51,54,55] * general discussions between redox-type oxygen-or electron-transfer mechanisms [12,16,28,31,34,35,39,…”