Novel La₃Fe(MoO₄)₆ phase: magnetic properties and ethanol reactivity

Abstract

Single crystals of a new oxide, La3Fe(MoO4)6, were grown from fluxes of oxide precursors, and a polycrystalline sample was also prepared by a standard solid state reaction. La3Fe(MoO4)6 crystallizes in the orthorhombic space group Pbca with unit cell parameters a = 19.3164(11), b = 10.4143(5) and c = 22.0594(12) Å. This crystal structure exhibits a singular architectural type built on infinite chains of Fe(MoO4)4, each of them being surrounded by two isolated MoO4 tetrahedra and three isolated La(3+) cations. Fe(3+) ions in La3Fe(MoO4)6 are antiferromagnetically ordered below TN = 6.6 K in chains and between chains, as refined from neutron diffraction data. Further the redox stability of this compound - pure powder - was checked using temperature-programmed X-ray diffraction under a controlled atmosphere; under air, we observed a reversible phase transition above 523 K. The same phenomenon was observed under a reductive atmosphere, followed by a destruction of the as-formed phase above 923 K owing to iron III to II reduction. Reactivity of ethanol was then evaluated to get insights into the redox properties of the material under working conditions. After 4 hours of reaction at 648 K, the ethanol conversion was 97% with a selectivity to acetaldehyde of ∼60%, the other products being formaldehyde (∼10%) and CO2 (∼30%), underlining a better acetaldehyde selectivity than that of the La-free conventional Fe2(MoO4)3 catalytic formulation.

Influence of Catalyst Acid/Base Properties in Acrolein Production by Oxidative Coupling of Ethanol and Methanol

“…[54] previously reported that formaldehydea nd CO x were observed with acetaldehyde when am ixture of ethanol/O 2 /He was fed over aF eMoLa catalyst. Colmonte tal.…”

“…Colmonte tal. [54] previously reported that formaldehydea nd CO x were observed with acetaldehyde when am ixture of ethanol/O 2 /He was fed over aF eMoLa catalyst. Probably,s ome CH 3 CH(OH)CH 2 COH aldol can be produced over FeMoO x or the aldolization catalyst.…”

Undulated oxo-centered layers in PbLn3O4(VO4) (Ln= La and Nd) and relationship with Nd4O4(GeO4)

“…The crucible was fitted with a platinum lid. It is interesting to note that, due to the refractory behaviour of lanthanum hydroxide, the flux growth technique is often preferred to isolate crystals of novel members [12], [14]. The combined choice of Pb 2+ and La 3+ is governed by their matching within oxo-centered tetrahedra (OPb 4 ) [15] (OBi 4 ) [16], [17] or (OCu 4 ) [18]… The "flexibility" induced by highly polarizable lone pair Pb 2+ species is another key-parameter, this cation being susceptible of sizeable Pb-O distances and the inherent possibility for mixed oxo-centred units, for example in O(Pb,Bi) 4 [19], [20], or O(Pb,Cu) 4 [21].…”