Óxidos defeituosos baseados em β-fosfatos de tri-cálcio (β-TCP) e alumina nanoestruturadas: propriedades catalíticas em reações de conversão de glicerol e metano

Abstract

Defects in crystalline materials confer unique physicochemical properties that enable their application in heterogeneous catalysis. In this sense, the insertion of a heteroatom with an ionic radius and/or valence different from that of the intrinsic atom favors synergistic effects, resulting in the formation of active catalytic sites, such as Lewis or redox sites. This work aims to synthesize defective oxides based on β-Ca3(PO4)2 containing Co, Cu, and Ni and γ-Al2O3 doped with Mg, Zn, and La. The structural, surface, acid-base, and textural properties of the synthesized solids will be used in the transformation of organic molecules. The insertion of transition metals (Cu and Co) into the β-Ca3(PO4)2 structure promoted a decrease in the lattice parameters, resulting in a compact structure with structural defects. The increase in the content of these metals led to the formation of extra-lattice phases, such as CuO and Co3O4, while low concentrations led to the formation of solid solutions. These modifications directly influenced the surface, acid-base, and textural properties of the solids. In glycerol acetylation, the superior performance of Cu-doped catalysts was attributed to the contribution of Lewis acid sites related to the CuO and Cu2O extra-lattice phases, highlighting the importance of the nature of the species exposed on the surface of the materials. Furthermore, the defects act synergistically with the Cu species, increasing the catalytic activity of β-TCP based solids. The characteristics of binary systems containing modified γ-Al2O3 revealed that Mg sites were inserted into the structure, forming a solid solution; in contrast, the insertion of La and Zn generated extra-network phases, with part of the unsubstituted sites available on the surface of the mesoporous alumina. Extrinsic defects were therefore formed from the inclusion of Mg in the γ-Al2O3 structure. The characteristics of Ni-Pt/γ Al2-xMexO2-δ (Me = La, Mg, or Zn) solids were decisive for the activity of these materials in tri-reforming of methane reaction (TRM). The defects generated by the modification of alumina, especially in the Ni-Pt/AlMg sample, increased the conversion of CO2 and CH4. In general, the insertion of Mg, La, or Zn into the γ-Al2O3 structure improved the catalytic properties of the materials.