Synthesis of cobalt ferrite nanoparticles by constant pH co-precipitation and their high catalytic activity in CO oxidation

Abstract

A series of cobalt ferrite samples were synthesized from a metal nitrate solution at constant pH between 9 and 12 by the controlled co-precipitation method without any surfactant. Cobalt and iron nitrates and sodium hydroxide base were simultaneously dosed so that the pH was precisely controlled during co-precipitation. The samples were characterized by PXRD, SEM, TEM, BET, and TPR. Careful analysis of typical PXRD peak profiles suggested the presence of two different variants of cobalt ferrite, a nano-scale material giving rise to broad peak tails and a more crystalline material leading to a sharper central profile. Rietveld refinement could be used to quantify the relative amount of both nano and crystalline fractions in these samples indicating that their relative abundance can be controlled by the co-precipitation pH. TEM analysis further proved the presence of both crystalline and nanocrystalline region in the samples. The average crystallite size of the cobalt ferrite nanocrystallites was 4–5 nm. These samples exhibit high BET surface area, in the order of 200 m2 g^-1. The samples were tested for catalytic performance in the CO oxidation reaction. The surface area, reduction behavior, and catalytic performance of ferrites were dependent on the relative amount of both the crystalline and nanocrystalline phases

Continuous Hydrothermal Flow Synthesis of Co1–xNixFe2O4 (x = 0–0.8) Nanoparticles and Their Catalytic Properties for CO Oxidation and Oxygen Evolution Reaction

“…However, very recently a similarly low T 50 of 154 °C was also found to co‐precipitated samples and room temperature activity was observed. In the latter work, the high activity was associated with the presence of a nanocrystalline fraction of CoFe 2 O 4 and a very high BET surface area of 263 m 2 · g –1 …”

“…Ferrite oxides, well known for their magnetic applications,, are also attractive for use as catalysts in the oxygen evolution/reduction reaction (OER/ORR), carbon monoxide oxidation, and organic decomposition processes . The spinel‐type structure ( AB 2 O 4 , A and B are di‐ and trivalent metal cations) enables incorporating transition metal elements in a wide range of combinations, which provides versatile materials that can be tuned in composition, electronic structure and redox properties for specific catalytic applications.…”

Preferential Oxidation of CO over CoFe2O4 and M/CoFe2O4 (M = Ce, Co, Cu or Zr) Catalysts

“…The cobalt ferrite (CoFe 2 O 4 ) presents the inverse (or partially inverse) spinel structure in which an important part of the Co 2+ cations are located in the octahedral sites and corresponding part of Fe 3+ cations are tetrahedrally coordinated [11,12]. Such structure is proposed to provide a good level of CO oxidation activity to the ferrite, attributed to the formation of very active octahedral Co 3+ upon oxidation under the reactant stream [9], with respect to other analogous cobalt spinel formulations with the normal spinel structure [9,10,[13][14][15][16]. Few reports in the literature have studied cobalt ferrite-based catalysts for the CO-PROX process [17,18].…”

Estudo dos efeitos de estratégias de manipulação química e estrutural em catalisadores heterogêneos aplicados à hidrogenação de CO>sub<2>/sub< a metanol

“…É nesse contexto que a coprecipitação em pH constante ganha destaque. Diferentemente do método clássico convencional, essa variação propõe que o gotejamento da solução contendo os sais precursores do catalisador seja realizado em uma solução com pH já controlado em um valor de concentração de íons hidroxila que seja, no mínimo, alto o suficiente para a garantir a precipitação do hidróxido metálico que apresente o maior produto de solubilidade da mistura (MUNNIK;DE JONGH;DE JONG, 2015;THOMAS, J. et al, 2017).…”

“…Dessa forma, ocorrerá uma precipitação, praticamente simultânea, de todas as espécies metálicas presentes em solução na forma de seus respectivos hidróxidos garantindo que as diferenças de produto de solubilidade não gerem alta segregação entre as partículas dos diferentes elementos (THOMAS, J. et al, 2017).…”