Catalysts For Partial Oxidation Research Articles

Atomically dispersed MoNi alloy catalyst for partial oxidation of methane

The catalytic partial oxidation of methane (POM) presents a promising technology for synthesizing syngas. However, it faces severe over-oxidation over catalyst surface. Attempts to modify metal surfaces by incorporating a secondary metal towards C–H bond activation of CH4 with moderate O* adsorption have remained the subject of intense research yet challenging. Herein, we report that high catalytic performance for POM can be achieved by the regulation of O* occupation in the atomically dispersed (AD) MoNi alloy, with over 95% CH4 conversion and 97% syngas selectivity at 800 °C. The combination of ex-situ/in-situ characterizations, kinetic analysis and DFT (density functional theory) calculations reveal that Mo-Ni dual sites in AD MoNi alloy afford the declined O2 poisoning on Ni sites with rarely weaken CH4 activation for partial oxidation pathway following the combustion reforming reaction (CRR) mechanism. These results underscore the effectiveness of CH4 turnovers by the design of atomically dispersed alloys with tunable O* adsorption.

Nano-crystalline NiO-MgO/NiAl2O4 catalyst for coking free low temperature partial oxidation of methane

Here, we report an ultra-small-sized nano-crystalline NiO-MgO/NiAl2O4 catalyst for coking-free partial oxidation of methane reaction at low temperature (450 °C). The catalyst was tested in a packed-bed reactor over a temperature range of 350 to 850 °C. The NiO-MgO/NiAl2O4 catalyst was optimized for calcination temperature and nickel content. The best-optimized sample was then tested for different gas hourly space velocities (GHSVs), resulting in 99 % CH4 conversion and varying H2/CO selectivities from 90 % to 70 % at 450 °C. A stability test was conducted at 500 °C for 100 h for stream on reaction conditions, resulting in 95 % CH4 conversion, 90 % H2 selectivity, and 60 % CO selectivity without any significant deactivation. The excellent catalytic activity and stable performance were attributed to the ultra-small size and nanocrystalline structure of NiO-MgO, as well as the presence of lattice oxygen reservoirs. Additionally, the synergistic interaction between the NiO-MgO solid solution and the support NiAl2O4 contributed to these properties.

ABO3 perovskite catalyst screening for chemical looping methane partial oxidation from descriptor-based microkinetic analysis

DFT calculations and descriptor-based microkinetic analysis have been performed to screen ABO3 perovskite catalysts for methane partial oxidation. The scaling relations indicate the adsorption energies of H@O and CH3@B have the capability of representing the energetics of methane oxidation, and bulk oxygen vacancy formation energy is identified to be a better single descriptor of the kinetics. The resultant volcano-shaped plot shows the catalytic activity varies in the order LaMnO3 > LaFeO3 > LaCoO3 ≈ LaCrO3, which agrees with the experimental findings and thus validates our theoretical predications. By screening 667 combinations of A- and B-cations based on electron neutrality, structural tolerance factors, and experimental verification, 77 ABO3 have been identified to be stable. Of them, SrRuO3, SmRhO3, LaIrO3, NdRhO3, and BaOsO3 are located at the summit of the volcano, which also exhibit satisfactory CO selectivity and enhanced carbon resistance compared to LaFeO3, and may act as the oxygen carrier candidates.

Ni-doped TiO2 supported Pt single-atom catalyst for partial oxidation of ethylene glycol to high-value chemicals in alkaline media

Pt-based electrocatalysts are usually used in several catalytic reactions. However, its high cost, scarcity, and susceptibility towards poisonous intermediate species highly limit these catalysts' large-scale applications. Downsizing catalysts to single-atom scale (SAC) have fascinated extensive research interests due to their higher activity, selectivity, and stability. Herein, we prepared highly active, selective, and poisoning-tolerant PtSACs on Ni-doped TiO2 support (PtSAC-Ni0.1Ti0.9O2). Ni in the catalyst creates a suitable environment to adsorb more OH− and make Pt accessible and ready for further oxidations. Thus, it exhibits higher electrocatalytic performance towards EGO than PtSAC-TiO2 does. It is also by far better than PtNP– Ni0.1Ti0.9O2. The higher catalytic performance by PtSAC-Ni0.1Ti0.9O2 is due to the synergistic effects of Ni and Pt. The catalyst selectively produces glycolate, formate, and hydrogen. Glycolate and formate are high-value chemicals for domestic uses or as inputs for industries to produce other chemicals. The catalyst also shows excellent Faradaic efficiency (>98 %) and stability towards EGO in alkaline media. The strong metal-support interactions between the catalyst and the support retard the agglomeration of the single atoms, thereby increasing their stability.

FexOy Nanoparticles Doped Spinel Nickel Aluminate as Partial Oxidation Catalyst: Synthesis, Characterization and Catalytic Evaluation

FexOy Nanoparticles Doped Spinel Nickel Aluminate as Partial Oxidation Catalyst: Synthesis, Characterization and Catalytic Evaluation

Mesoporous configuration effects on the physicochemical features of hierarchical ZSM-5 supported cobalt oxide as catalysts in methane partial oxidation

Hierarchical porous system has become a prevalent method to overcome the diffusion limitation of conventional zeolites. Two types of mesopores characterized as intra-crystalline (mesopores in the zeolite pore wall) and inter-crystalline mesopores (meso-sized voids between nano-zeolite aggregates) could be formed in the synthesis of hierarchical zeolites. In an attempt to investigate the influence of mesopores structure on the physicochemical properties of hierarchical ZSM-5, specifically cobalt oxide impregnated ZSM-5 zeolite samples with intra- and inter-crystalline mesopores were synthesized through two different synthesis strategies. Analysis of the physicochemical properties of the as-modified hierarchical ZSM-5 catalysts were carried out using SEM, TEM, XPS, and H2-TPR which showed distinct features given by the two mesopores configurations. Co-oxide impregnated on ZSM-5 with inter-crystalline mesopores was dominated by Co(II) species, while Co-oxide/ZSM-5 showed a fair amount of Co(III) and Co(II). Furthermore, analysis of the catalytic activity was conducted using methane partial oxidation as a model reaction. With a variation in reaction time, various types of oxygenated products, i.e. methanol, formaldehyde, formic acid, and a small trace of carbon dioxide were observed. Catalytic results suggested that the Co-oxide/ZSM-5 material with inter-crystalline mesopores configuration is more active for the methane partial oxidation reaction compared to the Co-oxide/ZSM-5 with intracrystalline mesopores. This was confirmed by the formation of formaldehyde rather than methanol as the major product in the brief reaction time of 30 min.

Electron-Delocalization-Stabilized Photoelectrocatalytic Coupling of Methane by NiO-Polyoxometalate Sub-1 nm Heterostructures.

The oxidative coupling of methane to C2 oxygenates merits great scientific and technological potential yet remains a challenge due to its inferior selectivity. Subnanomaterials (SNMs) with "p-n-p-n"-type heteroconstructions feature enhanced external field coupling properties and tunable electronic structures, serving as promising catalysts for the selective partial oxidation of methane. Here we develop NiO-polyoxometalate (POM) subnanocoils with a thickness of 1.8 nm, showing excellent catalytic activity toward photoelectrochemical coupling of methane into a C2 product under mild conditions (1 bar, 25 °C) with a notable productivity (up to 4.48 mmol gcat-1 h-1) and a high selectivity (>99%). Under photoelectrochemical coupling, C-H bonds can be activated by NiO, and the resulted *COOH intermediates are stabilized by the delocalized electrons in POM clusters. The contiguous active sites of NiO and POM at the molecular level allow the in situ coupling of *COOH into oxalate. This work points out an economic way for the oxidation of methane under mild conditions and may enlighten the design of functional SNMs from fundamental standpoints.

Stable oxygen permeable membrane with Ce0.9Gd0.1O2-δ protective layer for syngas production

The stability of catalytic membrane reactors (CMRs) is crucial for the practical applications in chemical reaction processes. However, currently reported CMRs with perovskite-based oxygen permeable membranes usually show poor stability owing to the over-reduction of Co and Fe ions in perovskite lattice under harsh reducing gas atmospheres and the interaction between membrane and catalyst. Here we developed an oxygen permeable membrane Ce0.9Gd0.1O2-δ-SrCe0.5Fe0.5O3-δ (CGO-SCF) with Ce0.9Gd0.1O2-δ (CGO) protective layer to construct a catalytic membrane reactor packed with Ni/Al2O3 catalyst for partial oxidation of methane. The CGO dense protective layer can effectively avoid the over-reduction of Fe ions in perovskite under harsh reducing gas atmospheres and the interaction between perovskite and Ni/Al2O3. Benefiting from high stability and mixed ionic-electronic conductivity of CGO in a low oxygen partial pressure environment, the developed membrane reactor with a dense CGO thin film was successfully operated with a stable CH4 conversion of 87% and a H2/CO ratio of 2 over 200 h in harsh operating conditions. This strategy proposed here provides insights into the design of highly stable catalytic membrane reactor in harsh conditions.

Oxygen vacancies enriched Ni-Co/SiO2@CeO2 redox catalyst for cycling methane partial oxidation and CO2 splitting

Redox catalysts play a vital role in the interconversion of two significant greenhouse gases, CO2 and CH4, via chemical looping methane dry reforming technology. Herein, a series of transition metals-alloyed and core–shell structured Ni-M/SiO2@CeO2 (M = Fe, Co, Cu, Mn, Zr) redox catalyst were fabricated and evaluated in a gas–solid fixed-bed reactor for cycling CH4 partial oxidation (POx) and CO2 splitting. The catalysts are composed of spherical SiO2 core and CeO2 shell, and the highly dispersed Ni alloy nanoparticles are the interlayer between core and shell. The oxygen vacancy concentration of Ni-M/SiO2@CeO2 followed the order of Co > Cu > Fe > Mn > Zr, and Ni alloying with transition metals significantly enhanced oxygen storage capacity (OSC). Ni-Co/SiO2@CeO2 catalyst with abundant oxygen vacancies and a high OSC showed the lowest temperatures of CH4 activation (610 °C) and CO2 decomposition (590 °C), thus demonstrating excellent redox reactivity. The catalyst exhibited superior activity and structural stability in the continuous CH4/CO2 redox cycles at 615 °C, achieving 87% CH4 conversion and 83% CO selectivity. The proposed catalyst shows great potential for the utilization of CH4 and CO2 in a redox mode, providing a new sight for design redox catalyst in chemical looping or related fields.

Partial oxidation of dimethoxymethane to syngas over granular and structured Pt-based catalysts

The catalytic properties of supported Pt-containing catalysts for dimethoxymethane partial oxidation (DMM PO) into syngas was studied in a tubular fixed bed reactor at atmospheric pressure and relatively low temperatures (∼300–500 °C). Comparative studies of granular 0.5–1.9 wt % Pt/Ce0.75Zr0.25O2–δ and structured 0.08 wt% Pt/8 wt% Ce0.75Zr0.25O2–δ/6 wt% η-Al2O3/FeCrAl catalysts in DMM PO were performed. The SEM and STEM HAADF techniques were used for catalyst characterization. The structured catalyst was proved promising for producing syngas by the DMM PO reaction for SOFC feeding applications. In particular, at atmospheric pressure, temperature 400 °C, and the reaction mixture (28.6 vol% DMM, 14.3 vol% O2, 57.1 vol% N2) feed rate of 5 L/(g·h), this catalyst provided complete conversion of DMM and O2 to syngas with a total H2 and CO content of 69 vol% and syngas productivity of ∼8 L/(g · h).

Improving the Coke Resistance of Ni-Ceria Catalysts for Partial Oxidation of Methane to Syngas: Experimental and Computational Study.

The synthesis of syngas (H2 : CO=2) via catalytic partial oxidation of methane (CPOM) is studied over noble metal doped Ni-CeO2 bimetallic catalysts for CPOM reaction. The catalysts were synthesized via a controlled deposition approach and were characterized using XRD, BET-surface area analysis, H2 -TPR, TEM, Raman and TGA analysis. The catalysts were experimentally and computationally studied for their activity, selectivity, and long-term stability. Although the pure 5Ni/CeO2 catalyst showed high initial activity (∼90%) of CH4 conversion, it rapidly deactivates around 20% of its initial activity within 140 hours of TOS. Doping of Ni/CeO2 catalyst with noble metal was found to be coke resistant with the best-performing Ni-Pt/CeO2 catalyst showed ∼95% methane conversion with >90% selectivity at a temperature of 800 °C, having exceptional stability for about 300 hours of time-on-stream (TOS). DFT studies were performed to calculate the activation barrier for the C-H activation of methane over the Ni, Ni3 Pt, Ni3 Pd, and Ni3 Ru (111) surfaces showed nearly equal activation energy over all the studied surfaces. DFT studies showed high coke formation tendency of the pure Ni (111) having a very small C-C coupling activation barrier (14.2 kJ/mol). In contrast, the Ni3 Pt, Ni3 Pd, and Ni3 Ru (111) surfaces show appreciably higher C-C coupling activation barrier (∼70 kJ/mol) and hence are more resistant against coke formation as observed in the experiments. The combined experimental and DFT study showed Ni-Pt/CeO2 as a promising CPOM catalyst for producing syngas with high conversion, selectivity and long-term stability suited for future industrial applications.

Lanthanide modified Pt/CeO2-based catalysts for methane partial oxidation: Relationship between catalytic activity and structure

In most cases, reasonable design and construction of Pt/CeO2-based catalysts and detailed exploration of relationship between its structural characteristics and the catalytic activity are crucial to improve the catalytic performance and reduce the cost. In this work, a series of CeO2 doped with lanthanide metal ions (La, Nd, Er and Yb) has been successfully synthesized, and then Pt is introduced through impregnation. The morphology, structure and component analysis are characterized by SEM, TEM (HRTEM), EDS, XRD, ICP-AES, XPS, UV Raman, O2-TPD, H2-TPR and CO or O2-pulse chemisorption, and the corresponding catalytic performances are developed by partial oxidation of methane. On the basis of the analysis of the structural properties of various catalysts, it is found that the Pt/CeLa catalyst shows the best catalytic performance due to its low valence state of Pt, excellent oxygen migration capacity and oxygen storage capacity, T50 is 510 °C and the selectivity is superiority. What's more, the modification of CeO2 by lanthanide metal ions especially La3+ can effectively change the oxygen activity of supports, so that this catalyst can be used in various redox catalytic reactions.

Cobalt–Samarium Oxide Composite as a Novel High-Performance Catalyst for Partial Oxidation and Dry Reforming of Methane into Synthesis Gas

The paper describes a novel high-performance catalyst that was developed for partial oxidation of methane (POM) and dry reforming of methane (DRM) into synthesis gas. The catalyst is based on samarium cobaltite dispersed in a samarium oxide matrix. Unlike its known counterparts based on samarium cobaltate, the novel catalyst is resistant to carbonization and contains active sites that exhibit higher syngas productivity.

Cobalt–Samarium Oxide Composite as a Novel High-Performance Catalyst for Partial Oxidation and Dry Reforming of Methane into Synthesis Gas

The paper describes a novel high-performance catalyst that was developed for partial oxidation of methane (POM) and dry reforming of methane (DRM) into synthesis gas. The catalyst is based on samarium cobaltite dispersed in a samarium oxide matrix. Unlike its known counterparts based on samarium cobaltate, the novel catalyst is resistant to carbonization and contains active sites that exhibit higher syngas productivity.

Mordenite-stabilised rhenium catalyst for partial oxidation of methane to syngas

A proton-type mordenite facilitates the reduction of hepta-valent Re species. The reduced Re species show a good catalytic activity toward the direct partial oxidation of CH4 to CO and subsequent reforming reactions.

Surface decoration of ceria nanoparticles as propane/air partial oxidation catalyst integrated in a micro-tubular solid oxide fuel cell

ABSTRACT In this study, a ceria (CeO2) support, synthesized using a hydrothermal method, was decorated with nano-sized Ni-particles using an impregnation method. A micro-tubular solid oxide fuel cell (MTSOFC) was integrated with a corundum tube, in which the Ni-CeO2 (10 wt% Ni) served as the catalyst for partial oxidation (POX). Using propane and air, there was no noticeable deactivation in the MTSOFC over a 48-h period. The maximum power density (MPD) was 0.57 W cm −2 at 700°C using propane and air (12.3 vol% propane), which is 0.01 W cm−2 higher than the cell using 20 vol% of hydrogen (0.56 W cm −2). When using propane and air as fuel and operating at 700°C, MPD values for intermediate and inlet current collector modes were 0.57 and 0.48 W cm−2, respectively. Carbon deposition at the fuel inlet was determined to be the primary cause of low current collection efficiency.

Bayesian-Optimization-Based Improvement of Cu-CHA Catalysts for Direct Partial Oxidation of CH4

Bayesian-Optimization-Based Improvement of Cu-CHA Catalysts for Direct Partial Oxidation of CH₄

In situ surface chemical properties and catalytic performances of Pt/CeO2 catalyst in methane partial oxidation under different conditions

The changes of oxygen vacancies and Pt valence on ceria supported precious metals materials often occur in methane partial oxidation reaction, leading to catalyst and reactivity variability. In this work, in situ X-ray photoelectron spectroscopy were used to investigate the surface chemical properties under no or different gas-phase oxygen concentrations and reaction temperatures, then the correlation between the chemistries with reaction performance were proposed. When only methane is present, reactive oxygen on catalyst surface are the oxygen source for methane oxidation. The oxygen vacancies on catalyst are abundant and part of Pt is reduced to zero valence. However, when the mixture of methane and oxygen is present at low temperature, gas-phase oxygen cannot be utilized directly, but could absorb on the oxygen vacancies and Pt, making oxygen vacancies reduction and Pt oxidation. Only when the temperature is higher than 400 °C, it can be converted into reactive oxygen species to participate in reaction, simultaneously, oxygen vacancy generation and Pt reduction, promoting the reaction continuous. Before the reaction begins, it is necessary to keep the catalyst rich in oxygen vacancies and metallic state of Pt for methane conversion at low temperature. The research is helpful to design catalysts and improve reactivity.

Collision dependent silver nucleation regulated by chemical diffusion and reaction

Nucleation is widely present in nature, from food production to haze generation. Owe to the spatiotemporal limitation in catching the dynamic characters of nucleation process, the theoretical development and the control technique of nucleation is far behind the demand. Here we report a strategy of controlling nucleation process via manipulating the collision of nucleation units, with the aim of disclosing the mechanism dominating the nucleation process. Silver nucleation is simulated at different collision conditions which is regulated by chemicals diffusion and reaction rate. It is found that the nucleation rate has a good linear relationship with the collision frequency, suggesting a collision dependent nucleation model. This model is evaluated by particles-based silver aggregation and validated by experiments conducted in an in-situ electron microscopy. Furthermore, the model is applied to the improved synthesis of silver catalysts for selective partial oxidation of ethylene.

Sub-nanometer Copper Clusters as Alternative Catalysts for the Selective Oxidation of Methane to Methanol with Molecular O2.

The partial oxidation of methane to methanol with molecular O2 at mild reaction conditions is a challenging process, which is efficiently catalyzed in nature by enzymes. As an alternative to the extensively studied Cu-exchanged zeolites, small copper clusters composed by just a few atoms appear as potential specific catalysts for this transformation. Following previous work in our group that established that the reactivity of oxygen atoms adsorbed on copper clusters is closely linked to cluster size and morphology, we explore by means of DFT calculations the ability of bidimensional (2D) and three-dimensional (3D) Cu5 and Cu7 clusters to oxidize partially methane to methanol. A highly selective Eley-Rideal pathway involving homolytic C-H bond dissociation and a non-adsorbed radical-like methyl intermediate is favored when bicoordinated oxygen atoms, preferentially stabilized at the edges of 2D clusters, are available. Cluster morphology arises as a key parameter determining the nature and reactivity of adsorbed oxygen atoms, opening the possibility to design efficient catalysts for partial methane oxidation based on copper clusters.