Environmental blue CoAl2O4 pigment co-doped by Zn2+ and Mg2+: synthesis,structure and optical properties

ABSTRACT

Nano-sized blue solid solutions Zn_xMg_0.5?xCo_0.5Al₂O₄ (x?=?0–0.5) have been synthesised by the Pechini method. Single-phase Zn_xMg_0.5?xCo_0.5Al₂O₄ with crystallite size of ～40?nm was identified by XRD measurement. The TG-DSC results indicated that the phase formation temperature of Zn_xMg_0.5?xCo_0.5Al₂O₄ increased with the substitution of Zn²⁺/Mg²⁺?→?Co²⁺ proceeding. The UV–vis spectra illustrated that the Zn_0.3Mg_0.2Co_0.5Al₂O₄ pigment displayed the most intensive blue colour with the strongest absorbance appearing within the visible region. The FT-IR spectra suggested that the inversion degree of Zn_xMg_0.5?xCo_0.5Al₂O₄ pigment reduces with the increase of Zn²⁺ rather than Mg²⁺, enabling to control the pigment colour by tuning the Zn²⁺ content. The FE-SEM images showed an irregular shaped morphology of Zn_xMg_0.5?xCo_0.5Al₂O₄ crystal, different from the cubic-like morphology of CoAl₂O₄ crystal. The XPS results illustrated that the inversion of pure CoAl₂O₄ pigment is larger than that of Zn_0.3Mg_0.2Co_0.5Al₂O₄. Both Zn_0.2Mg_0.3Co_0.5Al₂O₄ and Zn_0.3Mg_0.2Co_0.5Al₂O₄ show commercial potential in pigments application.     

Spinel-base cobalt-containing paint

The properties of spinel with Mg_0.1Co_0.9Al₂O₄ composition obtained by precipitation of hydroxides from aqueous solutions of magnesium, aluminum, and cobalt nitrates and calcination of the residue at a temperature of 500–1000°C were investigated. The results on cobalt metallization on porcelain articles decorated with cobalt paint produced by the Gzhel Company and paint synthesized from Mg_0.1Co_0.9Al₂O₄ spinel with an additive of cobalt oxide are presented. It was established that at a firing temperature of 1350–1380°C. the synthesized paint exhibits the first signs of cobalt metallization at a concentration of 15 mg/cm². whereas in the paint from the Gzhel Company, cobalt metallizes at a concentration of 5 mg/cm².Translated from Steklo i Keramika, No. 3, pp. 12–14, March, 1996.     

Catalytic synthesis of carbon nanostructures using layered double hydroxides as catalyst precursors

Layered double hydroxides with different components but similar iron content such as Fe_0.1Mg₂Al_0.9, Fe_0.1Zn₂Al_0.9 and Fe_0.1Cu₂Al_0.9 were prepared using a coprecipitation reaction. Then mixed oxides were obtained by calcination of these layered double hydroxide precursors, and their catalytic activities were examined during synthesis of various carbon nanostructures. It was found that single-walled carbon nanotubes were synthesized using a Fe_0.1Mg₂Al_0.9 mixed oxide catalyst, while multi-walled carbon nanotubes and carbon nanofibers resulted from Fe_0.1Zn₂Al_0.9 and Fe_0.1Cu₂Al_0.9 mixed oxides as catalysts, respectively.     

Influence of Co3O4, Fe2O3 and SiC on microstructure and properties of glass foam from waste cathode ray tube display panel (CRT)

Abstract

In the present study, the effect of temperature and oxidising agents such as Fe₂O₃ and Co₃O₄ on physical and mechanical properties of glass foam is investigated. The glass foam is made of panel glass from dismantled cathode ray tubes and SiC as a foaming agent. In the process, powdered waste glass (mean particle size below 63 μm) in addition to 4 wt-% SiC powder (mean particle size below 45 μm) are combined with Fe₂O₃ and Co₃O₄ (0·4, 0·8 and 1·2 wt-%) have been sintered at 950 and 1050°C. The glass foamed containing 1·2 wt-% Co₃O₄ has good physical properties, with porosity more than 80% and bending strength more than 1·57±0·12 MPa. However, by adding different amounts of Fe₂O₃ in comparison with samples without iron oxide, little changes in porosity and strength are obtained.     

Electric and dielectric study of cobalt substituted MgMn nanoferrites synthesized by solution combustion technique

Cobalt substituted Mg–Mn nanoferrites with formulae Mg_0.9Mn_0.1Co_xFe_2?xO₄, x=0.0, 0.1, 0.2 and 0.3, have been synthesized for the first time by the solution combustion technique. The effects of Co²⁺ ions on the dc resistivity, dielectric constant and dielectric loss tangent of Mg–Mn nanoferrites at room temperature are presented in this paper. X-ray diffraction confirmed the formation of a single phase spinel structure. Particle size was found to increase, 20.9–23.9 nm, with increasing Co²⁺ concentration. The dc resistivity was increased by two order of magnitude with substitution of Co²⁺ ions while the dielectric constant was found to be decreasing with the increasing concentration of cobalt ions. The value of dc resistivity obtained for Mg_0.9Mn_0.1Fe₂O₄ nanoferrite in our work is greater than the value obtained for the same composition prepared by the conventional ceramic technique. Further, the dielectric constant and dielectric loss tangent were observed to be decreasing with the increase in frequency.     

Sintering behavior and microstructure of (1-x)MgAl2O4-xMg2TiO4 spinel solid solutions prepared by isostructural heterogeneous nucleation

Magnesium aluminate (MgAl₂O₄) spinel has grasped considerable attention in high-temperature application by right of its excellent properties. However, the poor sintering behavior of MgAl₂O₄ is detrimental to its further development. In the present work, the application of isostructural heterogeneous nucleation method provides a novel idea for optimizing the sintering behavior of refractory materials. A series of (1-x)MgAl₂O₄-xMg₂TiO₄ (x = 0, 0.02, 0.04, 0.06, 0.08, and 0.1) spinel solid solutions with a present ration of components were fabricated from light calcined magnesia, reactive alumina and pre-preparation Mg₂TiO₄. The effect of Mg₂TiO₄ heterogeneous nucleating agent on the crystalline phase, densification, and microstructure evolution of MgAl₂O₄–Mg₂TiO₄ spinel solid solutions was studied. The XRD, XPS, and EDS results showed that Mg₂TiO₄ entered the lattice of MgAl₂O₄ to form a spinel solid solution, and the heterovalent substitution process was identified, where Ti⁴⁺ and Mg²⁺ ions of larger radius in the Mg₂TiO₄ replaced the Al³⁺ of smaller radius in the MgAl₂O₄. For the sample at x = 0.08, the spinel solid solutions exhibited the optimized densification with a relative density of 93.3%, an apparent porosity of 1.2%, and a compressive strength of 84.5 MPa. A significant increase in densification was related to the lattice distortion induced by ion size mismatch during the heterovalent substitution, thus accelerating the diffusion rate of Mg²⁺ and Al³⁺ ions in the spinelisation state. Moreover, the solid solubility content of Ti⁴⁺ in the MgAl₂O₄–Mg₂TiO₄ spinel solid solutions had a significant effect on the grain morphologies. The Mg₂TiO₄ heterogeneous nucleating agent significantly increased the spinelisation rate of MgAl₂O₄ spinel with negligible effect on densification.     

Synthesis and properties of Na<Subscript>0.55</Subscript>Co<Subscript>0.9</Subscript>M<Subscript>0.1</Subscript>O<Subscript>2</Subscript> (M = Sc,Ti, Cr–Zn,Mo, W,Pb, Bi) solid solutions

Ceramic samples of Na_0.55Co_0.9M_0.1O₂ (M = Sc, Ti, Cr–Zn, Mo, W, Pb, Bi) solid solutions are synthesized using the solid-phase method; their crystal structure parameters are determined; their microstructure, thermal expansion, thermal and electrical conductivity, and thermal e.m.f. are studied; and the values of their power factor and thermoelectric figure of merit are calculated. It is revealed that Na_0.55Co_0.9M_0.1O₂ cobaltites are p type conductors with the linear thermal expansion coefficient (LTEC) changed within limits of (12.2–16.2) × 10^–6 K^–1. The effect of the substitution of other metal cations for cobalt cations in Na_0.55CoO₂ on the parameters of the crystal structure, as well as the physicochemical and functional properties of Na_0.55Co_0.9M_0.1O₂ solid solutions, which are formed, is analyzed. It is shown that ceramic samples of the Na_0.55Co_0.9Cr_0.1O₂ and Na_0.55Co_0.9Bi_0.1O₂ compositions have the maximal power factor values among those studied at 0.917 and 1.018 mW/(m K²), respectively, at a temperature of 1100 K.     

Effect of the calcination temperature on the cation distribution and optical properties of Mg0.5Co0.5CrAlO4 spinel pigment

In this study, a blue-green pigment has been prepared by partially replace Co²⁺ and Cr³⁺ in CoCr₂O₄ spinel structure with Mg²⁺ and Al³⁺ using a gel casting method The gel precursor was calcined at various temperatures (900–1400 °C) to obtain Mg_0.5Co_0.5CrAlO₄ spinel pigment. Combining the Rietveld refinement method of XRD and peak fitting of XPS high-resolution spectra, the relationships between the cation distributions (Co²⁺, Mg²⁺, Al³⁺, and Cr³⁺) in the tetrahedron and octahedron of the spinel structure and the calcination temperature were examined. In the octahedron, the contents of Co²⁺ and Al³⁺ decreased with increasing calcination temperature, and the Mg²⁺ and Cr³⁺ contents exhibited the opposite trend. The bond lengths of A-O and B–O change with increasing calcination temperature, thereby leading to a change in the unit cell. The optical performance of the pigments was investigated via UV–vis and CIE L*a*b* spectrophotometry, and the study shows that the blue-green hue of the pigment powder is caused by the absorption at υ3～υ8 (370 nm–640 nm) in the visible light region. The varied contents of Co²⁺ and Cr³⁺ in the spinel structure among calcination temperatures cause the absorption spectrum intensity change, thereby resulting in various blue-green tones. This study lays the foundations for subsequent investigations of colour modification in Mg_xCo_1-xAl_yCr_2-yO₄ spinel.     

Sintering,hardness and cation inversion of nanocrystalline Beryllium – Magnesium aluminate ceramics

Beryllium-magnesium aluminate (Be_0.1Mg_0.9Al₂O₄ and Be_0.2Mg_0.8Al₂O₄) nanoparticles are synthesized by a coprecipitation method and sintered using Spark Plasma Sintering (SPS) to achieve near full density ceramics with grain sizes at the nanoscale. The sintered nanoceramics display grain sizes ranging from 14 to 33 nm, which are analyzed for optical transmission, Vickers hardness, and cation site inversion. When compared to Be-free MgAl₂O₄ nanoceramics, both Be_0.1Mg_0.9Al₂O₄ and Be_0.2Mg_0.8Al₂O₄ show transmissions ～30% lower at wavelength in the infrared range. The samples show a Vickers hardness of ～19.2 GPa with no apparent dependence on grain size. These values are consistently lower to those reported for beryllium-free MgAl₂O₄ spinel with similar grain size. ²⁷Al and ⁹Be Nuclear Magnetic Resonance (NMR) spectroscopy reveals that beryllium does not have a significant effect on cationic site inversion in the spinel and, similar to beryllium-free MgAl₂O₄, inversion remains solely a function of grain size. The results indicate beryllium ions form solid-solutions with MgAl₂O₄ spinel structure and do not alter the grain boundaries significantly enough to influence the mechanical properties of nanocrystalline ceramics.     

Sol–gel synthesis and infrared radiation property of Li-substituted cordierite

The Mg_2?xAl_4+1/2xLi_1/2xSi₅O₁₈ (0.1≤x≤1) ceramics with the substitution of (Li_1/2Al_1/2)²⁺ for Mg²⁺ were synthesized by the sol–gel method. The characterization of the modified cordierite included X-ray diffraction, SEM, EDS and infrared radiation. The crystal structure of Mg₂Al₄Si₅O₁₈ with the substitution of (Li_1/2Al_1/2)²⁺ for Mg²⁺ changed and the amount of secondary phase increased with increasing the x value from 0.1 to 1. High infrared emissivity over 0.9 in the band of 8–14 μm at room temperature was obtained in Mg_2?xAl_4+1/2xLi_1/2xSi₅O₁₈ (x=0.1). The material based on cordierite with x=0.1 sintered at 1200 °C maintained a single phase, compact microstructure and good infrared emissivity with potential use in infrared heating.     

Effect of compositional modifications on microstructure development and dielectric properties of Pb(Mg1/3Nb2/3)O3–PbTiO3 solid solutions

The effect of minor additions of excess MgO and PbO on the sintering characteristics, microstructure development and dielectric properties of perovskite-based Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ solid solutions was investigated. Both MgO and PbO are compatible with the Pb(Mg_1/3Nb_2/3)O₃-based solid solutions and thus, these phases co-exist with one another during sintering at elevated temperatures. On sintering a solid solution composition Pb[(Mg_1/3Nb_2/3)_0.9Ti_0.1]O₃ with minor additions of MgO, the excess MgO remained as a discrete phase in the ceramics at temperatures up to 1230 °C and inhibited grain growth. Above this temperature, MgO combined with the solid solution to form a liquid phase, which caused an enhancement of the densification process. On sintering the solid solution with excess PbO, a low-temperature melting PbO-rich liquid phase was formed, which promoted the densification process with inhomogeneous grain growth. Simultaneous additions of 1.0 wt.% MgO and 2.0 wt.% PbO to the Pb[(Mg_1/3Nb_2/3)_0.9Ti_0.1]O₃ solid solution and sintering the resulting material at 1000 °C for 3 h led to the formation of a dense and homogeneous microstructure consisting of evenly distributed grains with an average grain size of 10 μm. The peak dielectric constant of this composition (at ≈38 °C), measured at a frequency of 1 kHz, was 18,000 with a dissipation factor of <2%.     

Enhancement of the densification and thermal properties of Ca2Mg2Al28O46 ceramic by MnO addition

Ca₂Mg₂Al₂₈O₄₆ consists of platelet or platelet-like structural features derived from CaAl₁₂O₁₉. However, its application in dense structural materials is limited due to its poor sinterability and loose structure. In this work, Ca₂Mg₂Al₂₈O₄₆ ceramic was fabricated by solid-state reaction sintering, and the effects of MnO addition on the densification and thermal properties were investigated at 1600-1750 °C. The results showed that the Mn²⁺ solid dissolved into the Ca₂Mg₂Al₂₈O₄₆ lattice by the isovalent substitution of Mg²⁺ at 1650 °C, causing the grain morphology to change from hexagonal to equiaxed and resulting in a distorted magnetoplumbite structure. At 1700 °C, the solid solution reaction accelerated the densification, with the apparent porosity decreasing from 32.5% to 8.4% when 3 wt% MnO is added, promoted grain growth and pore discharge by increasing the number of lattice defects, grain boundary migration rate and in-situ stress. The enhanced thermal expansion coefficient and thermal conduction were mainly due to lattice expansion and grain coarsening. Moreover, the formation of trace amount of the secondary phase Mg_1-xMn_xAl₂O₄ also contributed to the improvement in the thermal properties.     

A comparative study of the magnetic and microwave properties of Al3+ and In3+ substituted Mg–Mn ferrites

The effect of substitution of diamagnetic Al³⁺ and In³⁺ ions for partial Fe³⁺ ions in a spinel lattice on the magnetic and microwave properties of magnesium–manganese (Mg–Mn) ferrites has been studied. Three kinds of Mg–Mn based ferrites with compositions of Mg_0.9Mn_0.1Fe₂O₄, Mg_0.9Mn_0.1Al_0.1Fe_1.9O₄, and Mg_0.9Mn_0.1In_0.1Fe_1.9O₄ were prepared by the solid-state reaction route. Each mixture of high-purity starting materials (oxide powders) in stoichiometric amounts was calcined at 1100 °C for 4 h, and the debinded green compacts were sintered at 1350 °C for 4 h. XRD examination confirmed that the sintered ferrite samples had a single-phase cubic spinel structure. The incorporation of Al³⁺ or In³⁺ ions in place of Fe³⁺ ions in Mg–Mn ferrites increased the average particle size, decreased the Curie temperature, and resulted in a broader resonance linewidth as compared to un-substituted Mg–Mn ferrites in the X-band. In this study, the In³⁺ substituted Mg–Mn ferrites exhibited the highest saturation magnetization of 35.7 emu/g, the lowest coercivity of 4.1 Oe, and the highest Q×f value of 1050 GHz at a frequency of 6.5 GHz.     

Improvement of electrochemical and thermal properties of Li[Ni0.8Co0.1Mn0.1]O2 positive electrode materials by multiple metal (Al, Mg) substitution

Al and/or Mg-substituted Li[Ni_0.8Co_0.1Mn_0.1−x−yAl_xMg_y]O₂ were prepared by a co-precipitation method and characterized by X-ray diffraction with Rietveld refinement, thermogravimetric analysis, differential scanning calorimetry (DSC), and electrochemical measurements. The Rietveld refinement results show that cation mixing of Al and/or Mg-substituted Li[Ni_0.8Co_0.1Mn_0.1−x−yAl_xMg_y]O₂ was reduced with increased doping amounts of Al and Mg. The Al and/or Mg substitution in Li[Ni_0.8Co_0.1Mn_0.1]O₂ also resulted in improved electrochemical cycling behavior, structural stability, and thermal stability compared to pristine Li[Ni_0.8Co_0.1Mn_0.1]O₂. The improvements of electrochemical and thermal properties resulted from the stabilized host structure by Al and/or Mg incorporation into Li[Ni_0.8Co_0.1Mn_0.1]O₂.     

Microstructure and thermal expansion of Al2TiO5–MgTi2O5 solid solutions obtained by reaction sintering

Solid solutions Mg_0.1Al_1.8Ti_1.1O₅ and Mg_0.5AlTi_1.5O₅ were obtained by reaction sintering of mixtures of the binary oxides at 1350–1600 °C using different precursor powders. For the composition Mg_0.1Al_1.8Ti_1.1O₅, ceramics sintered at 1400–1500 °C have high relative density (⩾90%), reduced grain size (2–6 μm), low thermal expansion (−0.8 to 0.3×10⁻⁶ K⁻¹ in the range 200–1000 °C) and reproducible expansion behaviour. At higher temperature, grain size rapidly increases owing to anisotropic and exaggerated grain growth (EGG) resulting in severe microcracking. Microstructure evolution is affected by the nature of the starting oxides, in particular for what concerns the onset temperature of EGG, the size and the fraction of abnormal grains. For the composition Mg_0.5AlTi_1.5O₅, EGG already takes place at 1350 °C and materials with grain size < 5 μm are difficult to obtain by conventional reaction sintering. Large grained samples (>10 μm) of both compositions show a reduced hysteresis and complex thermal expansion behaviour. In particular, heating to 1000 °C results in a significant increase in specimen size on return to room temperature. Repeated thermal cycling leads to an increase of the hysteresis.     

Mechanical and dielectric properties of porous magnesium aluminate (MgAl2O4) spinel ceramics fabricated by direct foaming-gelcasting

Porous ceramic materials have been broadly applied in various fields due to their multifunctional properties. Optimization of their microstructural characteristics, such as pore morphology, total porosity, and pore size distribution, which determine various properties of the final products, is crucial to improve their performances and thus extend their applications. In this study, single-phase porous MgAl₂O₄ materials were fabricated by direct foaming–gelcasting. With an increase in the foam volume from 260 to 350 mL, the total porosity and pore size of the porous ceramic increased, and its microstructure varied from mostly closed cells to open cells containing interconnected large pores (40–155 μm) and small circular windows (10–40 μm) in the ceramic skeleton. The total porosity could be tailored from 84.91% to 76.08% by modulating the sintering temperature and foam volume and the corresponding compressive strengths were in the range of 2.8–15.0 MPa. The compressive strength exhibited a power-law relationship with the relative density with indices of approximately 3.409 and 3.439, respectively. Porous MgAl₂O₄ ceramics exhibited low dielectric constants in the range of 1.618–1.910 at room temperature, which are well matched with theoretical calculations on account of a modified Bruggeman model. The porous MgAl₂O₄ ceramics with good mechanical and dielectric properties controlled easily by various sintering temperatures and foam volumes are promising for practical applications.     

Preparation and characterization of magnesium aluminate (MgAl2O4) spinel ceramic foams via direct foam-gelcasting

Lightweight MgAl₂O₄ spinel ceramic foams with high mechanical strength and good dielectric properties were prepared with a direct foam-gelcasting method using MgAl₂O₄ and TiO₂ (rutile phase, as sintering aid) powders. The effects of calcination temperature and foam volume on bulk density, apparent porosity, and on the mechanical and dielectric properties of the ceramic foams were investigated. Tailored porosity (75.14–82.46%), pore size (10–200 μm), dielectric constant (1.66–2.05), and compressive strength (4.0–14.3 MPa), were obtained based on the change of the foam volume in the foamed slurries, and the calcination temperature of porous ceramics. The compressive strength and dielectric constant of the as-manufactured spinel foam with a porosity of ~75.14% was as high as 14.3 MPa and 2.05, respectively. The spinel ceramic foam which had a porosity of 81.84% was prepared with a foam volume of 350 mL and a sintering temperature of 1500 °C, and exhibited heterogeneous pore structures, whereby large and open spherical cells involved in small circular windows on the internal walls with a mean pore size of ~66.26 μm and a grain size of ~8 μm. The experimental dielectric constant matches well with that calculated by the modified Bruggeman model. The dependence of the mechanical strength on the relative density can be represented by the Gibson and Ashby model. The fitted index values of the power relationship were 3.504 and 3.533, compared to the theoretical value of 1.5. The ceramic foam can potentially become a new type of electromagnetic wave-transmitting radome material due to its low dielectric constant (1.66–2.05) and dielectric loss (0.0026–0.006) values.     

Synthesis and properties of the composite ceramics from nanocrystalline Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-30% Y<Subscript>0.1</Subscript>Zr<Subscript>0.9</Subscript>O<Subscript>2</Subscript> prepared from a water-alcohol solution

The hydrogel of the mixed oxide Al₂O₃-30% Y_0.1Zr_0.9O₂ was prepared by precipitation of ammonia from a water-alcohol mixture (1 : 5). The Al₂O₃-30% Y_0.1Zr_0.9O₂ compound thus synthesized was characterized using differential scanning calorimetry, transmission electron microscopy, and the BET adsorption method. The obtained sample consisted of spherical particles with an average size of 16–20 nm and a specific surface area of 167 m²/g. The Al₂O₃-30% Y_0.1Zr_0.9O₂ powder was pressed at 300 MPa and then calcinated at 1600°C for 2 h in air. The topographic and structural features of the prepared ceramics were determined using atomic force microscopy and X-ray electron probe microanalysis. The porosity, the Vickers microhardness, and the tensile strength were determined by mercury porometry.     

Alumina and Alumina–Baria Supported Cobalt Catalysts for DeNO x : Influence of the Support and Cobalt Content on the Catalytic Performance

Co/Al₂O₃ and Co/Al₂O₃–BaO catalysts with low cobalt loading (0.1, 0.3 and 1 wt%) for the selective catalytic reduction (SCR) of NO _x by C₃H₆ were prepared. The distribution of cobalt species was investigated by UV–vis diffuse reflectance spectroscopy and by H₂-TPR in order to identify the active cobalt species in hydrocarbons (HC)-selective catalytic reduction (SCR). It was found that the nature of cobalt species strongly depends on the cobalt loading as well as on the properties of the support. The barium addition to the alumina slows down solid state diffusion processes, improving the thermal stability of the support and preventing diffusion of cobalt into the bulk. Highly dispersed surface Co²⁺ species over alumina were identified as active sites in the NO-SCR process. Accordingly, a high concentration of surface Co²⁺ sites in Co 1 wt%/Al₂O₃ improves the catalytic performance in NO-SCR, the long term stability as well as the water tolerance. On the contrary, the formation of Co₃O₄ particles in Co 1 wt%/Al₂O₃–BaO promotes the propylene oxidation by oxygen, decreasing the activity and selectivity of the catalyst in NO reduction.     

Ni‐Al2O3/Ni‐foam catalyst with enhanced heat transfer for hydrogenation of CO2 to methane

Monolithic Ni‐Al₂O₃/Ni‐foam catalyst is developed by modified wet chemical etching of Ni‐foam, being highly active/selective and stable in strongly exothermic CO₂ methanation process. The as‐prepared catalysts are characterized by x‐ray diffraction scanning electron microscopy, inductively coupled plasma atomic emission spectrometry, and H₂‐temperature programmed reduction‐mass spectrometry. The results indicate that modified wet chemical etching method is working efficiently for one‐step creating and firmly embedding NiO‐Al₂O₃ composite catalyst layer (～2 μm) into the Ni‐foam struts. High CO₂ conversion of 90% and high CH₄ selectivity of >99.9% can be obtained and maintained for a feed of H₂/CO₂ (molar ratio of 4/1) at 320°C and 0.1 MPa with a gas hourly space velocity of 5000 h^?1, throughout entire 1200 h test over 10.2 mL such monolithic catalysts. Computational fluid dynamics calculation and experimental measurement consistently confirm a dramatic reduction of “hotspot” temperature due to enhanced heat transfer. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4323–4331, 2015