Bulk Co3O4 for Methane Oxidation: Effect of the Synthesis Route on Physico-Chemical Properties and Catalytic Performance

The synthesis of bulk pure Co3O4 catalysts by different routes has been examined in order to obtain highly active catalysts for lean methane combustion. Thus, eight synthesis methodologies, which were selected based on their relatively low complexity and easiness for scale-up, were evaluated. The investigated procedures were direct calcination of two different cobalt precursors (cobalt nitrate and cobalt hydroxycarbonate), basic grinding route, two basic precipitation routes with ammonium carbonate and sodium carbonate, precipitation-oxidation, solution combustion synthesis and sol-gel complexation. A commercial Co3O4 was also used as a reference. Among the several examined methodologies, direct calcination of cobalt hydroxycarbonate (HC sample), basic grinding (GB sample) and basic precipitation employing sodium carbonate as the precipitating agent (CC sample) produced bulk catalysts with fairly good textural and structural properties, and remarkable redox properties, which were found to be crucial for their good performance in the oxidation of methane. All catalysts attained full conversion and 100% selectivity towards CO2 formation at a temperature of 600 °C while operating at 60,000 h−1. Among these, the CC catalyst was the only one that achieved a specific reaction rate higher than that of the reference commercial Co3O4 catalyst.This research was funded by the Spanish Ministry of Science and Innovation (PID2019-107105RB-I00 AEI/FEDER, UE), Basque Government (IT1297-19) and the University of The Basque Country UPV/EHU (PIF15/335 and DOCREC21/23)

Beneficial effects of nickel promoter on the efficiency of alumina-supported Co3O4 catalysts for lean methane oxidation

In this work bimetallic Ni catalysts supported over Co-Al2O3 and monometallic Co-Al2O3 and Ni-Al2O3 catalysts were examined for the complete oxidation of methane. With a 30 % total metallic loading, the samples were synthesized by a sequential precipitation route. All samples were characterized by nitrogen physisorption, X-ray fluorescence, X-ray diffraction, Raman spectroscopy, scanning electron microscopy, scanning-transmission electron microscopy, X-Ray photoelectron spectroscopy, and temperature-programmed reduction with hydrogen and methane. Their catalytic performance was investigated in the temperature range of 200-600 degrees C with a space velocity of 60.000 h-1. The bimetallic catalysts showed a better behavior in the oxidation reaction than the monometallic counterparts, mainly due to the good dispersion of Ni on the surface of the Co-Al2O3 samples. This has enabled the insertion of Ni2+ ions into the cobalt spinel lattice, which in turn provoked an increase in the amount of Co3+ species, and a subsequent enhanced mobility of oxygen species in the spinel. In this sense, the 5Ni/25Co catalyst showed the best performance, thus reducing the value of the T50 by 25 degrees C with respect to the monometallic catalysts.This research was funded by the Spanish Ministry of Science and Innovation (PID2019-107105RB-I00 AEI/FEDER, UE), Basque Government (IT1509-22) and the University of The Basque Country UPV/EHU (DOCREC21/23). The authors wish to thank the technical and human support provided by SGIker (UPV/EHU). In addition, authors acknowledge the use of instrumentation as well as the technical advice provided by the National Facility ELECMI ICTS, node ‘Advanced Microscopy Laboratory’ at University of Zaragoza

Comparative Study of Strategies for Enhancing the Performance of Co3O4/Al2O3 Catalysts for Lean Methane Combustion

Spinel-type cobalt oxide is a highly active catalyst for oxidation reactions owing to its remarkable redox properties, although it generally exhibits poor mechanical, textural and structural properties. Supporting this material on a porous alumina can significantly improve these characteristics. However, the strong cobalt–alumina interaction leads to the formation of inactive cobalt aluminate, which limits the activity of the resulting catalysts. In this work, three different strategies for enhancing the performance of alumina-supported catalysts are examined: (i) surface protection of the alumina with magnesia prior to the deposition of the cobalt precursor, with the objective of minimizing the cobalt–alumina interaction; (ii) coprecipitation of cobalt along with nickel, with the aim of improving the redox properties of the deposited cobalt and (iii) surface protection of alumina with ceria, to provide both a barrier effect, minimizing the cobalt–alumina interaction, and a redox promoting effect on the deposited cobalt. Among the examined strategies, the addition of ceria (20 wt % Ce) prior to the deposition of cobalt resulted in being highly efficient. This sample was characterized by a notable abundance of both Co3+ and oxygen lattice species, derived from the partial inhibition of cobalt aluminate formation and the insertion of Ce4+ cations into the spinel lattice.This research was funded by the Ministry of Economy and Competitiveness (CTQ2016-80253-R AEI/FEDER, UE), Basque Government (IT1297-19) and the University of The Basque Country UPV/EHU (PIF15/335

Non-noble metal oxide catalysts for methane catalytic combustion : sonochemical synthesis and characterisation

The aim of this study was to obtain nanocrystalline mixed metal-oxide–ZrO2 catalysts via a sonochemically-induced preparation method. The effect of a stabiliser’s addition on the catalyst parameters was investigated by several characterisation methods including X-ray Diffraction (XRD), nitrogen adsorption, X-ray fluorescence (XRF), scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectrometer (EDS), transmission electron microscopy (TEM) and µRaman. The sonochemical preparation method allowed us to manufacture the catalysts with uniformly dispersed metal-oxide nanoparticles at the support surface. The catalytic activity was tested in a methane combustion reaction. The activity of the catalysts prepared by the sonochemical method was higher than that of the reference catalysts prepared by the incipient wetness method without ultrasonic irradiation. The cobalt and chromium mixed zirconia catalysts revealed their high activities, which are comparable with those presented in the literature

Effect of Residual Na+ on the Combustion of Methane over Co3O4 Bulk Catalysts Prepared by Precipitation

The effect of the presence of residual sodium (0.4 %wt) over a Co3O4 bulk catalyst for methane combustion was studied. Two samples, with and without residual sodium, were synthesized by precipitation and thoroughly characterised by X-ray diffraction (XRD), N-2 physisorption, Wavelength Dispersive X-ray Fluorescence (WDXRF), temperature-programmed reduction with hydrogen followed by temperature-programmed reduction with oxygen (H-2-TPR/O-2-TPO), temperature-programmed reaction with methane (CH4 -TPRe), ultraviolet-visible-near-infrared diffuse reflectance spectroscopy (UV-vis-NIR DRS), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). It was found that during calcination, a fraction of the sodium atoms initially deposited on the surface diffused and migrated into the spinel lattice, inducing a distortion that improved its textural and structural properties. However, surface sodium had an overall negative impact on the catalytic activity. It led to a reduction of surface Co3+ ions in favour of Co2+, thus ultimately decreasing the Co3+/Co2+ molar ratio (from 1.96 to 1.20) and decreasing the amount and mobility of active lattice oxygen species. As a result, the catalyst with residual sodium (T-90 = 545 degrees C) was notably less active than its clean counterpart (T-90 = 500 degrees C). All of this outlined the significance of a proper washing when synthesizing Co3O4 catalyst using a sodium salt as the precipitating agent.This research was funded by the Ministry of Economy and Competitiveness grant number [CTQ2016-80253-R] and the University of the Basque Country UPV/EHU (PIF15/335)

On the Effect of the Synthesis Route of the Support in Co3O4/CeO2 Catalysts for the Complete Oxidation of Methane

Six ceria supports synthesized by various synthesis methodologies were used to deposit cobalt oxide. The catalysts were thoroughly characterized, and their catalytic activity for complete methane oxidation was studied. The supports synthesized by direct calcination and precipitation with ammonia exhibited the best textural and structural properties as well as the highest degree of oxidation. The remaining supports presented poorer textural properties to be employed as catalytic supports. The cobalt deposited over the first two supports presented a good dispersion at the external surface, which induced a significant redox effect that increased the number of Co3+ ions on their surface. Consequently, the presence of highly active lattice oxygen species on the surface of these catalysts was favored. Additionally, the optimal active catalyst (Co-DC) revealed a significant resistance to water vapor inhibition, owing to the high hydrophobicity of the ceria support.Spanish Ministry of Science and Innovation (PID2019-107105RB-I00 AEI/FEDER, UE and PDC2022-133897-I00), Basque Government (IT1509-22), University of the Basque Country UPV/EHU (DOCREC21/23

Analysis of heat and mass transfer limitations for the combustion of methane emissions on PdO/Co3O4 coated on ceramic open cell foams

Coated ceramic open cells foams (OCFs) with catalysts offer an attractive alternative to packed bed reactors for process intensification. Here, the effect of 3 wt.% PdO on Co3O4 coated on three different OCF (alumina, silicon carbide and zirconia) was investigated toward the reaction of CH4 combustion in lean conditions. The OCFs were characterized by Raman spectroscopy and FESEM analysis. The operating regime of each OCF catalyst was investigated using a series of mass transfer resistances assuming pseudo first order reaction (large excess of oxygen). The thermal conductivity of OCF plays an important role on the overall performance of the combustion reaction in terms of heat and mass transfer. The best OCF structured catalyst was tested up to 250 hours of time-on-stream, demonstrating good stability. PdO dispersion over the structured catalyst at the fresh and aged status was assessed by STEM analysis