Binary Oxides Prepared by Microwave-Assisted Solution Combustion: Synthesis, Characterization and Catalytic Activity

Abstract

Three different alumina-based Ni, Cu, Co oxide catalysts with metal loading of 10 wt %, and labeled 10Ni–Al, 10Co–Al and 10Cu–Al, were prepared by microwave-assisted solution combustion. Their morphological, structural and surface properties were deeply investigated by complementary physico-chemical techniques. Finally, the three materials were tested in CO oxidation used as test reaction for comparing their catalytic performance. The 10Cu–Al catalyst was constituted of copper oxide phase, while the 10Ni–Al and 10Co–Al catalysts showed the presence of “spinels” phases on the surface. The well-crystallized copper oxide phase in the 10Cu–Al catalyst, obtained by microwave synthesis, allowed for obtaining very high catalytic activity. With a CO conversion of 100% at 225 °C, the copper containing catalyst showed a much higher activity than that usually measured for catalytic materials of similar composition, thus representing a promising alternative for oxidation processes.

Synthesis, Characterization and Catalytic Activity of Ternary Oxide Catalysts Using the Microwave-Assisted Solution Combustion Method

“…No crystalline phases corresponding to Co x O y could be observed. The absence of any diffraction peaks of NiO or Co x O y phases, in Ni− or Co-containing catalysts, indicates the diffusion of cobalt and nickel into the γ−Al 2.67 O 4 lattice, producing NiAl 2 O 4 and CoAl 2 O 4 phases [ 16 , 17 ]. Meanwhile, no detectable peaks of alloy systems were observed on the three studied samples, suggesting that there is no interaction between the couples of transition metal species.…”

“…The synthesis of the three catalysts was carried out in the same manner as outlined in previous works [ 16 , 17 ]. At first, metal nitrate hydrates were dissolved in 10 mL of demineralized water.…”

“…The solution combustion route is a well-established method to prepare mixed oxide catalysts. This method has been successfully applied to prepare Ni–, Cu– or Co−γ−Al 2 O 3 catalyst systems [ 16 , 17 , 18 , 19 , 20 ]. These studies have assisted in providing valuable insights into the bulk and surface properties of the prepared catalysts.…”

“…These studies have assisted in providing valuable insights into the bulk and surface properties of the prepared catalysts. In our previous works [ 16 , 17 ], it has found that Cu oxides do not interact with γ−alumina and develop three dimensional crystallites, whose properties are similar to those of large bulk crystals. Differently, Ni or Co oxides interact with γ−alumina to form MAl 2 O 4 “surface spinels” and MAl 2 O 4 solid solution.…”

“…The activity of Ni–, Cu– or Co−γ−Al 2 O 3 catalyst systems in the total oxidation of CO has been extensively studied. In most cases, the formation of metal aluminates species was accompanied with a significant decrease in CO oxidation activity [ 17 ]. This trend was explained by the fact that the solid–solid interaction between γ−Al 2 O 3 and the transition metal oxide affects the state of the transition metal, thus affecting the catalytic activity in CO oxidation.…”