Study of Cesium or Cesium-Transition Metal-Substituted Keggin-Type Phosphomolybdic Acid as Isobutane Oxidation Catalysts

The structure of molybdenum-heteropoly acids under conditions of gas-phase selective oxidation catalysis: a multi-method in situ study

“…migration of Mo cations, partial reduction, modified short-range coordination) also take place under partial oxidation reaction conditions in both the free heteropoly acid and the cesium salt. This structural evolution under reducing conditions may be in agreement with a core-shell model under selective oxidation reaction conditions [26] where the cesium salt acts as nucleus coated by the molybdenum salified heteropoly acid. Because of the same lattice constant and structure, epitaxial orientation of the cesium salt and the molybdenum salified HPA should be feasible.…”

“…It has been proposed that the active phase of the HPA under reaction conditions corresponds to the intact and undistorted Keggin structure and, hence, that the catalytic reactivity of the material could be understood based on the initial structure of the HPA [22,23]. Conversely, the stability of the Keggin anions during thermal treatment and under catalytic conditions, the homogeneity of the partially salified HPA, and the correlation of the structure of the HPA and its catalytic activity are under debate [24,25,26,27]. Mixed phases of partially salified HPA have been proposed forming a core-shell system of the Cs 3 A-salt and the free acid under catalytic conditions [25].…”

Synthesis, Characterization and Catalytic Performance of a Novel Picolinic Acid-12-Molybdophosphoric Acid Hybrid Catalyst

“…Pure HPM shows the characteristic pattern in the Keggin polyanion that matched with literature very well. 18,26 The diffraction peaks of PI-HPM were observed mainly in the four ranges of 2q = 6-10, 16-20, 25-30 and 33-35 o , so it can be deduced that PI-HPM still maintained the Keggin structure of raw HPM. 27 But PI-HPM exhibited very different diffraction peaks from that of raw HPM and no diffraction peaks of HPI were detected, suggesting that PI-HPM was a new crystal phase but not the simple mixture of HPM and HPI.…”

“…17,18 Therefore, supported HPAs and salts of HPAs are developed to overcome the abovementioned problems. [2][3][4][17][18][19][20] Although these technologies can obviously improve the separation problem of HPAs from reaction system, the acid strength of supported HPAs and salts of HPAs was commonly lower than that of bulk HPAs. 21 The supported HPAs materials also suffered from the leaching of HPAs active species in polar reaction media.…”

Cu or Fe Modified Cs2HPMo12O40 as Catalysts for Selective Oxidation of Methacrolein

“…Some other studies have pointed that the addition of copper and iron as counter cations into the POMs-catalysts can improve catalytic performance, as copper and iron play an important role in the redox processes [13,14]. Langpape et al [15] found that the Cu 2+ /Cu redox couple could enhance the redox of the solids when protons were substituted by copper cations. The same effect of Fe was also confirmed [3].…”