Structural features of AgCaCdMg2(PO4)3 and AgCd2Mg2(PO4)3, two new compounds with the alluaudite-type structure, and their catalytic activity in butan-2-ol conversion

AgCaCdMg2(PO4)3 and AgCd2Mg2(PO4)3, two new compounds with the alluaudite-type structure, were synthesized by a solid state reaction in air at 750 °C. The X-ray powder diffraction pattern of AgCaCdMg2(PO4)3 indicates the presence of small amounts of (Ca, Mg)3(PO4)2 with the whitlockite structure, as impurity, whereas AgCd2Mg2(PO4)3 is constituted by pure alluaudite. The Rietveld refinements of the X-ray powder diffraction patterns indicate an ordered cationic distribution for AgCd2Mg2(PO4)3, with Ag on A(2)′, Cd on A(1) and M(1), and Mg on M(2), whereas a disordered distribution of Cd and Ca between the A(1) and M(1) sites is observed for AgCaCdMg2(PO4)3. The catalytic properties of these compounds has been measured in reaction of butan-2-ol dehydrogenation. In the absence of oxygen, both samples exhibit poor dehydrogenation activity. All samples displayed no dehydration activity. Introduction of oxygen into the feed changed totally the catalytic behavior of the catalysts. The production of methyl ethyl ketone increases with time on stream and the reaction temperature. AgCaCdMg2(PO4)3 is more efficient than AgCd2Mg2(PO4)3.