Activity Of Catalysts Research Articles

NON-OXIDATIVE METHANE CONVERSION STUDY ON GRANULATED Mo-CONTAINING ZEOLITE CATALYSTS

The results of the study of the influence of the method of forming granular Mo-containing zeolite catalysts on their physicochemical and catalytic properties in the process of non-oxidative conversion of methane are presented. There is shown a higher catalytic activity of granular catalysts with a hierarchical porous structure, obtained without using binders, compared to a granular catalyst obtained by a conventional method of mixing powdered zeolite with pseudobemite, followed by granulation and calcination. The texture and acid characteristics of granulated zeolites and Mo-containing catalysts based on them have been studied. The effect of dealumination of granular zeolites with a hierarchical porous structure on their texture and acid characteristics, as well as on their catalytic activity in the process of methane conversion is shown. The HRTEM method shows a difference in the distribution of the active Mo-containing phase in the granulated zeolite catalysts depending on the method of their preparation. Particles with a wide size distribution (2-30 nm), which are the crystalline phase of molybdenum carbide (β-Mo2C), and Mo-containing clusters in zeolite channels are present on the surface of granular samples that do not contain a binder. The catalyst prepared with the addition of the binder is micron agglomerates consisting of sub-micron sized zeolite particles and alumina sufficiently uniformly covering the surface of the zeolite. According to elemental mapping using energy dispersive X-ray spectroscopy, it was found that the active component is uniformly distributed over the catalyst surface, but the molybdenum signal on the alumina is significantly higher, which is explained by its higher specific surface area and the availability of particles. It has been found that the method of preparing granular Mo-containing zeolite catalysts has an effect on their catalytic activity, selectivity and stability in the process of non-oxidative conversion of methane to aromatic hydrocarbons. For citation: Stepanov A.A., Korobitsyna L.L., Vosmerikov A.V., Gerasimov E.Yu., Ishkildina A.Kh. Non-oxidative methane conversion study on granulated Mo-containing zeolite catalysts. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 8. P. 85-94. DOI: 10.6060/ivkkt.20246708.7t.

Unraveling Thermal Depolarization Phenomena in Biphasic Polarized Calcium Phosphate Catalyst

AbstractPermanently polarized biphasic calcium phosphate composed of hydroxyapatite and brushite (pp‐HAp/Bru), which is prepared by applying the thermally stimulated polarization treatment to calcined HAp, is used as a sustainable catalyst to transform CO2 into value‐added products. In this work, the stability of pp‐HAp/Bru is studied from structural, electrical, and catalytic perspectives, applying a thermal depolarization process with temperatures (Td) ranging from 200 to 1000 °C. Results show that the Bru phase is not stable when Td ≤ 400 °C, while the structure of the HAp refines and transforms into Bru when Td ≥ 600 °C. Besides, the electrical resistance and capacitance of the pp‐HAp/Bru increase with Td, evidencing the progressive electrical depolarization of the material. Thermal depolarization also influences the specific orientation of the OH– ions, which is partially lost (≈50%). All such changes affect the catalytic efficiency of pp‐HAp/Bru, which is proven using a reaction that transforms CO2 gas into acetic acid and formic acid. Results show that the total reaction yield linearly decreases with increasing Td. Based on such observations, a simple process is designed that allows the reconstitution of the structure and restores the activity of such green catalysts.

Atomically dispersed Rh active sites on MOF-5 via defect engineering for hydroformylation of n-butene

This work explored the role of defective sites on the hydroformylation of n-butene through ligand regulation. The investigation examined the effect of modulator properties on defect sites and rhodium loading, and optimized the H2BDC/modulator ratio to improve catalyst activity. Atomically dispersed Rh is anchored to these highly dispersed defect sites, effectively preventing aggregation and thereby enhancing hydrogenation ability. Under optimal conditions, the catalyst achieved a conversion of 96.9 %, with an overall aldehyde selectivity of 90 %. DRIFTS analysis provided compelling evidence that Rh(CO)2 and HRhCO species were formed on 1Rh/MOF-5-HBC, improving CO insertion capability. This study highlights the significance of MOFs as catalyst supports in enhancing performance through defect engineering. The ability of the modulator to induce defect formation was measured by pKa. Meanwhile, it has been discovered that the length differences between the modulator and the MOF organic ligand can have a significant impact on the stability of defective MOFs.

Step-by-step enhancing oxygen evolution ability of CoFe2O4 by hybrid structure engineering and fluorine doping

CoFe2O4 is a very promising platform to catalyze oxygen evolution reaction (OER). Herein, the largely enhanced intrinsic performance of CoFe2O4 derived from the ZIF-67 for OER was demonstrated by step-by-step hybrid structure engineering and fluorine doping (F-Co/CoFe2O4@NC). This electrode showed high surface area, rapid charge transfer ability, and catalytic kinetics compared to the CoFe2O4@NC and Co/CoFe2O4@NC catalysts. Specifically, an overpotential of 280 mV was required to drive a kinetic current density of 10 mA cm−2 (loading on glassy carbon electrode, no iR-correction), with a Tafel slope of 49.7 mV dec-1 and remarkable catalytic stability throughout a 50-hour test. Theoretical analysis revealed a charge redistribution among Co, and Fe atoms was triggered by fluorine doping, and a more rapid active phase of CoOOH was generated on the surface during catalysis as confirmed by in-situ Raman spectroscopy and the post-surface chemical state analysis. The stable F atoms were more likely to be doped into CoFe2O4, and the active layer of CoOOH formed over the F-CoFe2O4 surface was more active than other states. Moreover, the electronic interaction induced by F-doping is more conducive to improving the adsorption energy of *OOH species, thereby improving the reaction kinetics and catalytic activity of OER. The current work showed an effective step-by-step approach to boosting the intrinsic activity of traditional catalysts for energy-relevant catalysis reactions.

Hydrogen generation from catalytic hydrolysis of ammonia borane with Co-Cu-B/g-C3N4/NF catalyst

In this study, different double-supported Co-Cu-B/g-C3N4/Ni foam (NF=Ni foam) catalysts were synthesized by chemical deposition method in a certain pH value range (pH value between 10.5 and 12.0). Their catalytic performances of hydrolyzing ammonia borane (NH3BH3) hydrolysis were investigated to produce hydrogen at 298 K. Because of the adding of g-C3N4 in the plating solution, the obtained sample had certain photocatalytic activity when the visible light was introduced the hydrolysis experiment. The results displayed that the as-prepared Co-Cu-B/g-C3N4/NF catalyst at pH = 10.5 exhibited an improved catalytic effect for NH3BH3 hydrolysis under visible light irradiation. The corresponding hydrogen generation rate reached 8893 mol·min−1·g−1, and the activation energy was 41.8 kJ·mol−1. The catalytic performance of Co-Cu-B/g-C3N4/NF catalysts prepared by this method is better than that of as-obtained mono-metal Co-B/g-C3N4/NF catalyst. More importantly, its activity has exceeded many single-carrier cobalt-based catalysts reported so far, and even some single-support precious metal catalysts for NH3BH3 hydrolysis. It indicated that the strategy of double carriers and introduction of light contributed to the improvement in catalytic activity for the non-noble metal-based catalysts during NH3BH3 hydrolysis.

Exploring dynamics in single atom catalyst research: A comprehensive DFT-kMC study of nitrogen reduction reaction with focus on TM aggregation

Transition metal (TM)-based single atom catalysts (SACs) have emerged as a promising solution for the electrochemical nitrogen reduction reaction (NRR) due to their unique d-orbitals and low coordination, which facilitate efficient N2 bond weakening and increased reactivity. However, conventional theoretical approaches fail to incorporate the kinetics of TM aggregation, a crucial factor in SAC systems that affects catalyst stability and activity over time. Addressing this, we combined kinetic evaluations with thermodynamic and electronic analyses on 216 SAC candidates, using boron carbon nitride (BCN) as a substrate. Our findings revealed that Cr anchored to BCN exhibits a high turnover frequency (3.1 × 10−6 s−1) under mild conditions (300 K, 1 bar), attributed to its minimal TM aggregation over time. This research not only fills the gap in kinetic research within the SAC field but also proposes a SAC candidate distinguished by its superior kinetics, thermodynamic, and electronic properties.

Process intensification in the continuous dehydrogenation of methylcyclohexane to toluene

The toluene/methylcyclohexane cycle is a safe and practical Liquid Organic Hydrogen Carrier (LOHC) for the storage of hydrogen. Nevertheless, the dehydrogenation reaction of methylcyclohexane (MCH) should be improved to assure a total selectivity to toluene (TOL), avoiding the subproducts formation. In this research, a millireactor with channel internal diameter in the range of milimeters has been tested and evaluated in the dehydrogenation of MCH to TOL. The millireactor configuration confers it some features and advantages compared to fixed-bed reactors, e.g., better mass and energy transfer and increased performance (10–20 %). To verify these advantages, a comparison between conventional fixed bed (9 mm i.d.) and millireactor is carried out. Thanks to its configuration, the millireactor could control effectively the heat generated by the reactions to avoid hot-spot formation and the sintering of the catalyst. The results obtained demonstrate that the catalysts activity in the reaction is improved with the application of the millireactor respect the fixed-bed ones and neither catalyst sintering, nor pressure drop was appreciated during the catalytic tests. At the best reaction conditions, Tecnalia´s millireactor converses continuously up to 99 % of MCH to TOL with 100 % selectivity at atmospheric pressure, showing the huge potential of the millireactor concept.

Efficient conversion of ethanol to acetaldehyde with induction heating at low temperature

The application of induction heating (IH) to provide heat for chemical reactions has received great attention due to its potential to electrify chemical reactions. Biomass-based production of acetaldehyde from ethanol has gained rising interest since it provides an alternative sustainable method instead of the fossil-fuel-based output using acetylene and formaldehyde in the presence of a catalyst. The dehydrogenation of ethanol can be catalyzed by supported copper catalysts. The reaction is typically carried out at high temperatures, around 250–300 °C, without oxygen. The resulting product mixture usually contains acetaldehyde, as well as other byproducts such as ethylene and hydrogen gas. The acetaldehyde can be separated from the other components using distillation or other separation techniques. In this work, we studied the catalyst activity with IH for the first time and achieved high ethanol conversion and acetaldehyde selectivity at a temperature of 30 ˚C lower than that with conventional furnace heating (CFH). A transport model was applied to design the catalyst bed configuration and improve the catalyst activity, stability, and energy efficiency by minimizing the temperature gradient. Our work suggests that the temperature distribution and the fast compensation of heat loss through IH are critical for the catalyst behavior. Both high production efficiency and energy efficiency can be achieved with IH, such that it can be an efficient and environment-friendly heating method for the chemical industry.

Synthesis of surface-engineered SrFe2O4 for efficient catalytic partial oxidation of methane

In this study, a series of platinum (Pt)-doped strontium iron oxide (SrFe2O4) catalysts with varying particle sizes were synthesized through the four different catalysis synthesis methods such as solution combustion synthesis (SCS), co-precipitation (Co-PPT), oxalic acid assisted sol-gel (OXA) and, hydrothermal (HT). The objective was to investigate the impact of particle size on the catalytic activity and long-term stability of these four catalysts. The XRD and Raman results confirmed the formation of the SrFe2O4 perovskite structure. HRTEM, SEM, and other characterizations revealed a clear correlation between the synthesis conditions and the resulting particle sizes. The highest%CH4 conversion was around 95 % for the catalyst prepared through Solution combustion synthesis and the catalyst was found to be thermally stable up to. 100 h at 800 °C with a negligible variation of conversion while maintaining the H2/CO ratio at 2.0. To gain insight into catalytic activity, stability, and selectivity of catalysts we have performed Temperature-programmed surface reaction (TPSR) at a controlled temperature ramping program. This study also includes the study of coke deposition on the spent catalysts through different characterization techniques. Furthermore, we have performed a kinetic study to find the initial rate of the reaction and the activation energy of the Pt-doped SrFe2O4 catalyst and it has been found that activation energy was 35 KJ/mol for the catalyst Pt/SrFe2O4 synthesis through the solution combustion method.

P-band regulation guides the free-standing porous carbon electrode for efficient Na-CO2 batteries

The Na-CO2 batteries with low-cost resources and high energy density have attracted huge attention in Mars and deep ocean exploration, but the slow CO2 reduction reaction (CO2RR) and CO2 evolution reaction (CO2ER) kinetics severely limit their practical application. Developing free-standing cathodes and understanding the relationship between the catalyst's active center and activity are essential to address long-standing challenges. This manuscript explores the promising metal-free porous carbon as a catalyst. The porous carbon network vertically grows on the surface of free-standing carbon paper to maximum exposure to the active site and optimization of electron/electrolyte transfer. Moreover, the active center of the carbon catalyst is optimized by introducing nitrogen or sulfur hetero-atom to regulate the p-band center, which steers the orbital hybridization and accelerates CO2RR and CO2ER kinetics The p-band optimized free-standing porous carbon electrode shows outstanding cycling of 1000 h with a small voltage gap of 1.04 V and a large energy efficiency of 71.2 % at 10 uA cm−2. This study provides a new strategy for designing and fabricating p-band guided free-standing electrodes aiming at high-performance and wearable Na-CO2 batteries.

Synergistic catalytic effect of titanium and iron incorporated to spherical MCM-41 in selective catalytic oxidation of diphenyl sulphide with H2O2

Spherical mesoporous silicas of MCM-41 type modified with titanium, iron or both these metals were prepared by co-condensation method and tested in the role of catalysts for selective oxidation of diphenyl sulphide with H2O2 to diphenyl sulphoxide and diphenyl sulphone. The monometallic catalysts containing titanium or iron were found to be active catalysts of diphenyl sulphide mainly to diphenyl sulphoxide. A very significant increase in catalytic activity was observed for the bimetallic samples, containing both titanium and iron. Moreover, in the case of bimetallic catalysts with higher titanium loading, diphenyl sulphone is a dominating reaction product. The increased activity of the bimetallic catalysts has been related to the synergistic operation of titanium and iron in conversion of hydrogen peroxide into reactive species, which in the next step oxidise diphenyl sulphoxide.

Tetragonal/orthorhombic phase Bi2WO6 homojunction for photoelectrochemical degradation of rhodamine B with high efficiency

Photoelectrochemical (PEC) degradation of organic pollutants to CO2 and H2O is a promising strategy to solve the growing environmental problems. Bismuth tungstate (Bi2WO6) has attracted much attention due to its good chemical stability and moderate conduction band valence band position. However, the PEC activity of Bi2WO6 catalysts is greatly limited due to its rapidly complex electron-hole. This article reports a rational low-cost design that successfully prepares tetragonal/orthorhombic Bi2WO6 homojunction on FTO conductive glass substrates through a simple two-step solvothermal method, significantly enhancing the PEC performance. The study investigated the effectiveness of photoelectrochemical degradation of the recalcitrant organic pollutant Rhodamine B (RhB) and conducted an in-depth exploration of the photoelectrocatalytic reaction process and mechanism. The experimental results indicate that the homojunction achieves a degradation rate of up to 100 % for the recalcitrant organic pollutant RhB within 30 minutes, significantly surpassing that of single-phase Bi2WO6, and at the same time the sample maintains good stability after five cycles of operation. Further analysis of the capture experiments indicates that holes (h+) and superoxide radicals (·O2⁻) are the primary active species responsible for RhB degradation. This study not only provides new insights into the design of high-efficiency photoelectrode, but also offers new solutions for environmental pollution control.

CeO2-Supported Single-Atom Cu Catalysts Modified with Fe for RWGS Reaction: Deciphering the Role of Fe in the Reaction Mechanism by In Situ/Operando Spectroscopic Techniques.

Reverse water-gas shift (RWGS) reaction has attracted much attention as a potential approach for CO2 valorization via the production of synthesis gas, especially over Fe-modified supported Cu catalysts on CeO2. However, most studies have focused solely on investigating the RWGS reaction over catalysts with high Cu and Fe loadings, thus leading to an increase in the complexity of the catalytic system and, hence, preventing the gain of any reliable information about the nature of the active sites and reaction mechanism. In this work, a CeO2-supported single-atom Cu catalyst modified with iron was synthesized and evaluated for the RWGS reaction. The catalytic results reveal a significant synergistic effect between CuCeO2 and Fe, demonstrating an activity up to three times higher than the combined catalytic activities of monometallic catalysts (Fe/CeO2 + CuCeO2) under identical conditions. Various ex situ and in situ/operando techniques are employed to unveil the concealed role of Fe in catalyst activity enhancement. The combined findings from hydrogen temperature-programmed reduction (H2-TPR) and operando electron paramagnetic resonance spectroscopy (EPR) reveal that the added Fe predominantly interacts with Cu-containing surface sites, resulting in the stabilization of higher proportions of Cu single sites. Near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and operando EPR results unveil a synergistic interplay of Fe with Cu-containing sites and CeO x domains, efficiently enhancing both the reoxidation of Cu+ in Cu+-Ov-Ce3+ moieties and the reducibility of Ce4+ in CeO x domains under RWGS conditions. Detailed mechanistic studies reveal that the RWGS reaction predominantly proceeds via the redox mechanism.

DFT and machine learning studies on a multi-functional single-atom catalyst for enhanced oxygen and hydrogen evolution as well as CO2 reduction reactions

In this contribution, the design of a graphene-supported high-entropy single-atom catalyst (HESAC) composed of Fe, Co, Ni, and Ru metal atoms (FeCoNiRu-HESAC) is proposed. Negative formation energy and positive dissociation potentials indicate such materials' thermodynamic and electrochemical stability. Based on density functional theory (DFT) calculations, Co active sites lead to the overpotentials of 0.28 VRHE for oxygen evolution reaction (OER), 0.16 VRHE for hydrogen evolution reaction (HER), and 0.25 VRHE for CO2 reduction reaction (CO2RR) towards CO formation. These surpass the activity of CoN4 single-atom catalyst. More interestingly, the low CO2RR and HER overpotentials enable the FeCoNiRu-HESAC to produce syngas (CO + H2). In addition, the Fe, Ni, and Ru sites simply serve as counterparts to modify the performance of Co active sites through non-bonding interactions. Besides, machine learning (ML) implies that, the valence electrons of intermediates as well as the d orbital electrons of metal sites are the most important parameters affecting the reaction intermediates’ Gibbs free energy. According to these DFT and ML results, a strategy to design multifunctional HESACs electrocatalysts is developed.

Regulating the cationic vacancy structure of NiO to optimize its d band center and accelerate oxygen evolution reaction

In order to study the influence of cationic vacancy structure on the oxygen evolution reaction (OER) activity of catalysts. A series of cationic vacancy NiO catalysts (d-Mx-NiO) with different vacancy structure were prepared by alkali-etching the doping amphoteric oxide element in this paper. Due to diverse intrinsic characteristic of doping amphoteric oxide element, the electronic configuration of cationic vacancy in d-Mx-NiO is changed after alkali-etching. Density functional theory (DFT) calculations reveal that the d band center of Ni element is increased gradually with the increasing valence state of doping vacancy element, which is beneficial to optimize the adsorption energy for the OER intermediate products. Among the d-Mx-NiO catalysts, d-Al0.2-NiO catalyst possesses the highest d band center and oxidation state of Ni, resulting in the superior OER performance with only 285 mV overpotential to achieve the current density of 10 mA cm−2. Additionally, d-Al0.2-NiO also demonstrates admirable stability after 100 h OER test with a ∼99% faradaic efficiency. The current finding would offer a valuable insights to design and fabricate the cationic vacancy OER catalysts with high efficiency.

The Role of The Ni/HZSM-5 Ratio on The Anisole Hydrodeoxygenation Reaction

ABSTRACT. Bio-oil is a renewable energy source with high oxygen levels, and anisole is a chemical widely employed in research to represent it. Catalytic hydrodeoxygenation (HDO) reduces the oxygen content. A catalyst known as nickel-modified HZSM-5 has shown promising results for HDO. Meanwhile, catalyst efficiency depends on the Ni/HZSM-5 ratio. So, this study aims to determine how the Ni/HZSM-5 ratio influences the catalyst's properties, activity, and selectivity in anisole HDO. The Ni/HZSM-5 catalyst was made using the wet impregnation method with various ratios of Ni/HZSM-5. The catalysts were analyzed for their morphology using scanning electron microscopy-energy-dispersive X-ray (SEM-EDX). The diffraction patterns were studied using X-ray diffraction (XRD). Surface area and porosity were determined through gas sorption analysis (GSA). Then, the acidity strength was evaluated via temperature-programmed ammonia desorption (NH3-TPD). The characterization results show Ni was successfully impregnated and distributed evenly in HZSM-5 without changing the primary structure. Adding Ni metal to HZSM-5 increases the surface area of the catalyst but reduces its acid strength. The catalytic performance of the catalysts was then evaluated in a flow reactor at 400 °C, using 15 mL/min H2 gas. The liquid products of the reaction were analyzed using gas chromatography-mass spectroscopy (GC-MS). The results of the catalytic performance show that Ni4.5/HZSM-5 has the highest catalytic activity in anisole conversion. At the same time, Ni6.4/HZSM-5 shows the highest selectivity towards benzene-toluene-xylene (BTX). Keywords: Hydrodeoxygenation, nickel, anisole, heterogeneous catalyst, acidity.

Experimental study of ammonia storage characteristics of selective catalytic reduction for diesel engine based on Cu-based catalysts

In this paper, the ammonia storage characteristics of Cu-based zeolite catalysts at different exhaust temperatures in heavy-duty diesel engines were experimentally investigated. The data such as exhaust temperature, rotational speed, torque, urea consumption, NOx concentration at selective catalytic reduction (SCR) inlet and outlet, ammonia storage, and NH3 leakage of the diesel engine were recorded respectively. The trend of ammonia storage characteristics of the SCR system was analyzed using the urea injection stopping time as the cut-off point. Both the SCR catalyst ammonia storage volume and the time to saturation of ammonia storage volume decreased with the increase in exhaust temperature. The maximum value of ammonia storage was 9.58 g at 193 °C and 1.08 g at 376 °C. The saturation time decreased from 466.4 s to 96.8 s. The increase in catalyst activity at high temperatures increased the rate of denitrification reaction, but it was observed that the ammonia slippage occurred earlier from 450 s to 100 s, which was mainly due to a more active ammonia desorption reaction at high temperatures. The larger ammonia storage at low temperatures made the effect on NOx conversion efficiency more significant, and the effect of exhaust temperature gradually increased when the temperature was further increased.

Pd nanoparticles supported on silver, zinc, and reduced graphene oxide as a highly active electrocatalyst for ethanol oxidation

In this manuscript, we present a facile approach to synthesize a highly active catalyst for the electro-oxidation of ethanol using Pd nanoparticles supported on a Ag–Zn alloy on reduced graphene oxide. This nanocomposite material was fabricated via a two-step process of incineration followed by sol-gel synthesis. The physical properties of the catalyst were evaluated using X-ray diffraction, X-ray photoelectron spectroscopy, and scanning and transmission electron microscopies. To understand the catalyst's activity for ethanol oxidation, we performed a series of cyclic voltammetry and electrochemical impedance spectroscopy experiments in alkaline medium. The catalyst exhibited good catalytic activity with a current density of 13.01 mA cm−2, a value seven times higher than the commercial standard Pd/C catalyst and higher than any other previously reported Pd-based catalyst. The results were attributed synergistic effects between the Pd and alloy support along with the large electrochemically active surface area of the material. Taken together, these results suggest that ethanol electrocatalysts based on nanocomposites of Pd, Ag, and Zn is promising candidates for future ethanol fuel cells.

Engineering Partially Oxidized Gold via Oleylamine Modifier as a High-Performance Anode Catalyst in a Direct Borohydride Fuel Cell.

Direct borohydride fuel cell (DBFC) is considered a promising energy storage device due to its high theoretical cell voltage and energy density. For DBFC, an Au catalyst has been used as an anode for achieving an ideal eight-electron reaction. However, the poor activity of the Au catalyst for borohydride oxidation reaction (BOR) limits its large-scale application because of the weak BH4- adsorption. We found, by density functional theory calculations, that the adsorption of BH4- on the oxidized Au surface is stronger than that on the metallic Au surface, which can promote the process of the oxidation of BH4- to *BH3 during the BOR. Here, we reported an oleylamine-modified partially oxidized Au supported on carbon powder (AuC-OLA) with a stable oxidation state. The obtained catalyst delivered a high peak power density of 143 mW/cm2, which is 2 times higher than that of a commercial 40% AuC (Pretemek). The in situ Fourier transform infrared studies showed that the activity of AuC-OLA for BOR is ascribed to the enhanced adsorption for BH4- on the partially oxidized Au surface. These findings will promote the reasonable design of efficient Au electrocatalysts for DBFCs.

Features of CO₂ Hydrogenation on MoO₃/Al₂O₃ and γ-Al₂O₃

The physicochemical and catalytic (CO₂ hydrogenation) characteristics of Mo-containing catalysts have been studied. Catalysts with an oxide content of Mo 8 and 15 wt% were prepared by impregnation with ammonium paramolybdate γ-Al₂O₃ followed by drying and calcining at 500°C. The introduction of Mo oxide reduces the pore volume of the support and increases their average size, which indicates the distribution of the deposited molybdenum oxide in the pores of the support. According to X-ray diffraction data, the calcined catalyst contains practically no crystalline MoO₃ phase. According to the Raman spectra, oxygen-containing formations are present on the catalyst surface, in which Mo atoms are tetrahedrally and octahedrally coordinated with respect to oxygen atoms. The impregnated MoO₃ oxide is partially reduced by hydrogen during linear heating starting from 320°C. Hydrogenation of CO₂ (gas of composition, vol.%: 30.7 CO₂, 68 H₂, rest. N2, sample 0.5 g) was studied in the mode of linear heating up to 400°C. The main reaction is the reverse reaction of CO steam reforming. The contribution of the methanation reaction to CO₂ hydrogenation is small. An increase in temperature and pressure has a positive effect on CO₂ conversion. With an increase in pressure from 1 to 5 MPa, the CO content increases approximately twofold. In the hydrogenation of CO₂, γ-Al₂O₃, preheated in a flow of H₂ to 400°C, also exhibits noticeable activity, although significantly lower compared to Mo-containing catalysts. With increasing pressure, the activity of aluminium oxide and Mo-containing catalysts, increases.