Hydrogen Temperature-programmed Desorption Research Articles

TDS Simulator: A MATLAB App to model temperature-programmed hydrogen desorption

We present TDS Simulator, a new software tool aimed at modelling thermal desorption spectroscopy (TDS) experiments. TDS is a widely used technique for quantifying key characteristics of hydrogen-material interactions, such as diffusivity and trapping. However, interpreting the output of TDS experiments is non-trivial and requires appropriate post-processing tools. This work introduces the first software tool capable of simulating TDS curves for arbitrary choices of material parameters and hydrogen trap characteristics, using the primary hydrogen diffusion and trapping models (Oriani, McNabb-Foster). Moreover, TDS Simulator contains a specific functionality for loading experimental TDS data and conducting the inverse calibration of a selected transport model, providing automatic estimates of the density and binding energy of each hydrogen trap type in the material. In its first version, TDS Simulator is provided as a MATLAB App, which is made freely available to the community and provides a simple graphical user interface (GUI) to make use of TDS Simulator straightforward. As reported in the present manuscript, the outputs of TDS Simulator have been extensively validated against literature data. Demonstrations of automatic determination of trap characteristics from experimental data through the optimisation tool are also provided. The present work enables an efficient and straightforward characterisation of hydrogen-material characteristics relevant to multiple applications, from nuclear fusion to the development of hydrogen-compatible materials for the hydrogen economy. TDS Simulator can be downloaded from https://mechmat.web.ox.ac.uk/codes (To be uploaded immediately after the review process).

Does the active surface area determine the activity of silica supported nickel catalysts in CO2 methanation reaction?

Two series of silica supported catalysts with comparable nickel contents varying from 2.5 to 20 wt.% were prepared by wet impregnation method in the absence and presence of citric acid in the impregnation solution. Temperature-programmed reduction, X-ray diffraction and electron microscopy studies indicated changes of reducibility of nickel oxide species in the corresponding catalysts and formation of nickel nanoparticles of different size and morphology. A gradual increase in the performance of catalysts in the CO2 methanation reaction was observed with increasing Ni loading. The application of a modified impregnation method led to a reduction in the size of the nickel crystallites, which increased the active surface area of the catalysts, improving their activity and selectivity towards methane at low temperatures, as well as their stability at high temperatures. It was shown that the high active surface area of silica-supported nickel catalysts, due to the presence of small crystallites, is a key factor in increasing their activity. However, other catalyst properties may also play an important role. Hydrogen temperature-programmed desorption and in-situ DRIFTS adsorption/desorption of CO, CO2 and CO2 hydrogenation reaction studies indicated that modification of the method of catalyst synthesis led to changes in the surface properties of the catalysts, affecting the way CO2 and H2 activation and the transformation of resulted intermediate species to the final reaction products.

Impact of CO hydrogenation diffusion limitation and cluster size on Fischer-Tropsch synthesis mechanism: An integrated experimental and theoretical study

This research examines how varying cobalt particle sizes and support pore sizes affect CO diffusion in Fischer-Tropsch synthesis (FTS). It explores cobalt catalysts deposited on perlite (P) and its modified version (S) with weight loadings ranging from 5% to 20%. N2 adsorption-desorption, BET analysis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), hydrogen temperature-programmed reduction (H2-TPR), hydrogen temperature-programmed desorption (H2-TPD), transmission electron microscopy (TEM), and Fourier-transform infrared spectroscopy (FT-IR) analyses were utilized for characterization. The results designate that higher cobalt loading on the modified support (S) decreases CH4 selectivity while enhancing selectivity towards C5+ hydrocarbons. Despite larger cobalt particles in 15CP compared to 15CS, 15CP exhibits higher CH4 selectivity and reduced C5+ selectivity because of CO diffusion limitations and smaller pore size. DFT calculations reveal product selectivity depends on FTS mechanism and cobalt cluster size influences reaction pathways, with smaller clusters favoring CO insertion and larger clusters favoring carbide mechanisms.

Constructing Ni-Pt Bimetallic Catalysts for Catalytic Hydrogenation and Rearrangement of Furfural into Cyclopentanone with Insight in H/D Exchange by D2O Labeling.

Developing a metallic catalyst for converting furfural (FAL) to highly valuable products such as cyclopentanone (CPO) is important for fine chemical synthesis by the efficient utilization of biomass resources. The presence of diverse unsaturated carbon atoms in FAL and the rearrangement of oxygen atoms hinder the production of CPO. We developed an optimal nickel (Ni)-to-platinum (Pt) molar ratio (1:0.007) for a bimetallic Ni-Pt/alumina (Al2O3) catalyst with a low Pt loading via an impregnation method to efficiently catalyze the selective hydrogenation of FAL in an aqueous solution to form CPO. The comprehensive characterizations by X-ray diffraction and X-ray absorption near edge structure analyses elucidated the formation of Ni0/Pt0 and Ni2+/Pt4+ after reduction by H2. The addition of a low amount of the Pt-Ni/Al2O3 catalyst resulted in an alleviation of H2 reduction behavior detected by hydrogen temperature-programmed reduction, accompanied by low H2 desorption ability observed by hydrogen temperature-programmed desorption. The catalytic activity of Ni-Pt/Al2O3 was higher than those of Ni/Al2O3 and Pt/Al2O3 catalysts. The maximum CPO yield was 66% with 93% FAL conversion under the optimized conditions (160 °C, 20 bar of H2 pressure, and 2 h). Isotopic deuterium oxide (D2O) labeling revealed the transfer of deuterium (D) atoms from D2O to the intermediates and products during hydrogenation and rearrangement, which confirmed that water was a medium for rearrangement and the source of hydrogen for the reaction. This study developed an efficient catalyst for the catalytic hydrogenation and ring rearrangement of FAL into CPO.

Liquid-phase hydrogenation of sunflower oil over platinum and nickel catalysts: Effects on activity and stereoselectivity

This study presents the results of comparative hydrogenation of sunflower oil over a platinum catalyst supported on activated diatomite and an industrial nickel catalyst (Pricat-9910). Catalysts are characterized using physical methods, such as transmission electron microscopic, temperature programmed hydrogen desorption, Brunauer–Emmett–Teller and inductively coupled plasma atomic emission spectrometry, enabling the determination of the size of catalyst particles, forms of adsorbed hydrogen, and specific surface area. Depending on the process conditions, hydrogenation reaction rates on platinum catalysts have been found to be 2–5 times higher than cis-trans isomerization reaction rates. Using a nickel catalyst, the hydrogenation and isomerization rates at low temperatures (110°C-130 °C) and 0.5 MPa pressure are almost similar, while, the hydrogenation rate is 1.4–1.8 times lower than the isomerization rate at high temperatures and pressures, leading to the formation of a large number of trans isomers. The difference in catalysts selectivity may be attributed the speciation and different adsorption energies of surface hydrogen, leading to the possibility of simultaneous hydrogenation of linoleic and oleic acids on the nickel catalyst.

Bimetallic CuPd nanoparticles supported on ZnO or graphene for CO2 and CO conversion to methane and methanol.

Carbon dioxide (CO2) and carbon monoxide (CO) hydrogenation to methane (CH4) or methanol (MeOH) is a promising pathway to reduce CO2 emissions and to mitigate dependence on rapidly depleting fossil fuels. Along these lines, a series of catalysts comprising copper (Cu) or palladium (Pd) nanoparticles (NPs) supported on zinc oxide (ZnO) as well as bimetallic CuPd NPs supported on ZnO or graphene were synthesized via various methodologies. The prepared catalysts underwent comprehensive characterization via high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDX) mapping, electron energy loss spectroscopy (EELS), X-ray diffraction (XRD), hydrogen temperature-programmed reduction and desorption (H2-TPR and H2-TPD), and deuterium temperature-programmed desorption (D2O-TPD). In the CO2 hydrogenation process carried out at 20 bar and elevated temperatures (300 to 500 °C), Cu, Pd, and CuPd NPs (<5 wt% loading) supported on ZnO or graphene predominantly yielded CH4 as the primary product, with CO generated as a byproduct via the reverse water gas shift (RWGS) reaction. For CO hydrogenation between 400 and 500 °C, the CO conversion was at least 40% higher than the CO2 conversion, with CH4 and CO2 identified as the main products, the latter from water gas shift. Employing 90 wt% Cu on ZnO led to an enhanced CO conversion of 14%, with the MeOH yield reaching 10% and the CO2 yield reaching 4.3% at 230 °C. Overall, the results demonstrate that lower Cu/Pd loading (<5 wt%) supported on ZnO/graphene favored CH4 production, while higher Cu content (90 wt%) promoted MeOH production, for both CO2 and CO hydrogenation at high pressure.

Highly dispersed Pt boosts active FexN formation in ammonia decomposition

Ammonia decomposition plays an important role in hydrogen production, especially in the context of a hydrogen economy. Fe-based catalysts are a popular choice due to their affordability and moderate activity, making them attractive for large-scale applications. However, the transformation of Fe-based catalysts into more active FexN species can be slow, resulting in a prolonged induction period. To address this issue, we investigated the effects of Pt addition on FexN formation in ammonia decomposition. Our results show that even a slight Pt addition significantly enhances the FexN formation rate, increasing it over threefold. Pt aids in H2 desorption via reverse spillover, which, in turn, exposes more Fe surface sites where nitridation occurs, leading to the formation of iron nitride. Characterization via High-angle annular dark-field imaging scanning transmission electron microscopy, X-ray diffraction, and in situ X-ray absorption spectroscopy (XAS) revealed the formation of Fe2N as active species, whereas temperature-programmed hydrogen desorption, temperature-programmed reduction by hydrogen, and in situ XAS supported the existence of H reverse spillover and spillover effects. Overall, our study provides an improved understanding of the active species formation mechanism of Fe catalysts in ammonia decomposition and offers a simple strategy for improving their catalytic performance.

Anisole Hydrodeoxygenation over Nickel-Based Catalysts: Influences of Solvent and Support Properties

The realization of biofuels and chemicals requires the development of highly active and selective catalysts, which are resistant to deactivation. A conventional ZSM-5 (SiO2/Al2O3 = 30) was modified with 0.2 M NaOH to generate a mesoporous zeolite support. The parent zeolite, mic-ZSM-5, the modified zeolite, hie-ZSM-5, and a mesoporous silica support, SiO2, were impregnated with 5% nickel and characterized using X-ray powder diffraction (XRD), Brunauer–Emmett–Teller (BET) analysis of nitrogen sorption, scanning electron microscopy with energy dispersive X-ray (SEM-EDX), transmission electron microscopy (TEM), hydrogen temperature-programmed reduction (H2-TPR), ammonium hydrogen temperature-programmed desorption (NH3-TPD), and thermogravimetric analysis (TGA). The influences of the support properties and solvent during the hydrodeoxygenation of anisole were investigated by measuring concentration profiles and rates in a high-pressure batch reactor. NaOH treatment significantly improved the pore structure, acidity of the support, and metal dispersion as well as the interaction of nonframework Ni species with zeolite and, hence, the catalytic activity and selectivity. The highest anisole conversion of 100% was obtained in 120 min over the hie-Ni/ZSM-5 catalyst with cyclohexane selectivity of 88.1%. In addition, the Ni/SiO2 catalyst was 84.5% selective to toluene at 48.9% anisole conversion in 120 min; as such, it was proposed that the transformation of anisole proceeds via either a direct deoxygenation–hydrogenation or isomerization–direct deoxygenation pathway. However, no substantial differences in anisole conversion or product selectivity were observed when decalin and n-decane were compared as solvents. A catalyst reusability test showed hie-Ni/ZSM-5 as the most stable of the three catalysts in terms of anisole transformation, even though the catalyst recorded the biggest weight loss of 9.2% suggesting high resistance to carbon deactivation. Therefore, with this very good catalytic activity, good selectivity to liquid product, and stability, the mesoporous Ni/ZSM-5 catalyst is a potential candidate for economically beneficial future industrial applications.

Modification of the synthesis of layered titanium chloride nitride

Layered titanium nitride chloride (TiNCl) exhibits a relatively high superconducting transition of ∼16 K, and it is a candidate for the unconventional superconductor. To better understand the superconductivity, we modified the synthesis process for TiNCl. Highly crystalline TiNCl was prepared by chemical vapor transport at different transport temperatures and intercalated with sodium (Na) metal. Although the crystallographic parameters obtained through Rietveld refinement are similar, the superconducting properties strongly depend on the treatment temperature of pristine TiNCl. Optical and photoemission spectroscopy revealed an in-gap state below the Fermi level, indicating hydrogen incorporation, similar to the case of β−ZrNCl. Hydrogen temperature-programmed desorption revealed hydrogen emission against the heat treatment of the obtained pristine TiNCl. The in-gap state of hydrogen inhibits the introduction of electron carriers from the intercalated Na metal.

Co Loading Adjustment for the Effective Obtention of a Sedative Drug Precursor through Efficient Continuous-Flow Chemoselective Hydrogenation of 2-Methyl-2-Pentenal

This work presents the effect of Co loading on the performance of CNR115 carbon-supported catalysts in the continuous-flow chemoselective hydrogenation of 2-methyl-2-pentenal for the obtention of 2-methylpentanal, an intermediate in the synthesis of the sedative drug meprobamate. The Co loading catalysts (2, 6, 10, and 14 wt.%) were characterized by Brunauer–Emmett–Teller (BET) surface area analysis, transmission electron microscopy (TEM), H2 temperature-programmed reduction (H2-TPR), temperature-programmed desorption of hydrogen (H2-TPD) analysis, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy for selected samples, and have been studied as hydrogenation catalysts at different pressure and temperature ranges. The results reveal that a certain amount of Co is necessary to achieve significant conversion values. However, excessive loading affects the morphological parameters, such as the surface area available for hydrogen adsorption and the particle size, preventing an increase in conversion, despite the increased presence of Co. Moreover, the larger particle size, caused by increasing the loading, alters the chemoselectivity, favouring the formation of 2-methyl-2-pentenol and, thus, decreasing the selectivity towards the desired product. The 6 wt.% Co-loaded material demonstrates the best catalytic performance, which is related to the formation of NPs with optimum size. Almost 100% selectivity towards 2-methylpentanal was obtained for the catalysts with lower Co loading (2 and 6 wt.%).

Palladium-copper membrane prepared by electroless plating for hydrogen separation at low temperature

Pd-based membranes are often used to purify hydrogen, but often fail as a result of phase changes at low temperatures. In this study, an electroless plated Pd-Cu membrane was produced to purify hydrogen generated during various low temperature processes. The membrane was fabricated by sequential electroless plating of Pd and Cu with hydrazine as a reducing agent, followed by alloying in a hydrogen atmosphere. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) analyses confirmed that the Pd-Cu layer was successfully alloyed, and thickness of the alloy layer was 23.74 µm. The hydrogen permeability of the Pd-Cu membrane prepared in this work was significantly increased compared to the previously published results. The hydrogen permeation flux of 0.6 m3 m−2 h−1 for the Pd-Cu membrane was stable over a period of 10 h at 175 °C without suffering hydrogen embrittlement and was stable over a temperature cycle. Finally, hydrogen temperature-programmed desorption (H2-TPD) confirmed that the desorption properties of hydrogen were changed by using this Pd-Cu alloy.

Chemical and Structural Changes by Gold Addition Using Recharge Method in NiW/Al2O3-CeO2-TiO2 Nanomaterials.

NiWAu trimetallic nanoparticles (NPs) on the surface of support Al2O3-CeO2-TiO2 were synthesized by a three-step synthetic method in which Au NPs were incorporated into presynthesized NiW/Al2O3-CeO2-TiO2. The recharge method, also known as the redox method, was used to add 2.5 wt% gold. The Al2O3-CeO2-TiO2 support was made by a sol–gel method with two different compositions, and then two metals were simultaneously loaded (5 wt% nickel and 2.5 wt% tungsten) by two different methods, incipient wet impregnation and ultrasound impregnation method. In this paper, we study the effect of Au addition using the recharge method on NiW nanomaterials supported on mixed oxides on the physicochemical properties of synthesized nanomaterials. The prepared nanomaterials were characterized by scanning electron microscopy, BET specific surface area, X-ray diffraction, diffuse reflectance spectroscopy in the UV–visible range and temperature-programmed desorption of hydrogen. The experimental results showed that after loading of gold, the dispersion was higher (46% and 50%) with the trimetallic nanomaterials synthesized by incipient wet impregnation plus recharge method than with impregnation plus ultrasound recharge method, indicating a greater number of active trimetallic (NiWAu) sites in these materials. Small-sized Au from NiWAu/ACTU1 trimetallic nanostructures was enlarged for NiWAu/ACT1. The strong metal NPs–support interaction shown for the formation of NiAl2O4, Ni-W-O and Ni-Au-O species simultaneously present in the surface of trimetallic nanomaterial probably plays an important role in the degree of dispersion of the gold active phase.

Copper-Promoted Cobalt/Titania Nanorod Catalyst for CO Hydrogenation to Hydrocarbons

The effect of Cu on cobalt/titania nanorod (Co/TNR) catalysts for the promotion of carbon monoxide (CO) hydrogenation to hydrocarbons was investigated. Varying amounts of Cu (1.5–6.0 wt%) were loaded onto the base Co/TNR catalyst using the deposition–precipitation method. Characterization by X-ray diffraction (XRD) revealed that the Cu particles were well dispersed over the Co/TNR catalysts. Characterizations by temperature-programmed desorption of hydrogen (H2-TPD) and carbon monoxide (CO-TPD) and temperature-programmed reduction in hydrogen (H2-TPR) proved the effect of the Cu promoter in the Co/TNR catalyst by its bimetal effect with Co, where the Co/TNR catalysts containing Cu generally showed a significant improvement in comparison with the base Co/TNR catalyst not containing the Cu promoter. The CO and H2 adsorption capacities and reducibility were optimal on the catalyst containing 1.5% Cu (1.5Cu-Co/TNR). This aligns well with the catalytic activity performance of all the catalysts, where the 1.5Cu-Co/TNR catalyst exhibited the best performance, yielding 16.8% CO conversion and 57.7% C5+ hydrocarbon selectivity at 240 ℃ and 5 bar.

Hydrogenative Cyclization of Levulinic Acid to γ-Valerolactone with Methanol and Ni-Fe Bimetallic Catalysts

A series of Ni-Fe/SBA-15 catalysts was prepared and tested for the catalytic hydrogenation of levulinic acid to γ-valerolactone, adopting methanol as the only hydrogen donor, and investigating the synergism between Fe and Ni, both supported on SBA-15, towards this reaction. The characterization of the synthesized catalysts was carried out by XRD (X-ray powder diffraction), TEM (transmission electron microscopy), H2-TPD (hydrogen temperature-programmed desorption), XPS (X-ray photoelectron spectroscopy), and in situ FT-IR (Fourier transform–infrared spectroscopy) techniques. H2-TPD and XPS results have shown that electron transfer occurs from Fe to Ni, which is helpful both for the activation of the C=O bond and for the dissociative activation of H2 molecules, also in agreement with the results of the in situ FT-IR spectroscopy. The effect of temperature and reaction time on γ-valerolactone production was also investigated, identifying the best reaction conditions at 200 °C and 180 min, allowing for the complete conversion of levulinic acid and the complete selectivity to γ-valerolactone. Moreover, methanol was identified as an efficient hydrogen donor, if used in combination with the Ni-Fe/SBA-15 catalyst. The obtained results are promising, especially if compared with those obtained with the traditional and more expensive molecular hydrogen and noble-based catalysts.

MoP with rich species generated via radio frequency thermal plasma for higher alcohols synthesis from syngas

In this paper, the molybdenum phosphide (MoP) catalysts (TPR-MoP and TPR-MoP-Pla) were prepared by the traditional method and the RF (radio frequency) thermal plasma technique respectively and characterized by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM), hydrogen temperature-programmed desorption (H2-TPD) and carbon monoxide temperature-programmed desorption (CO-TPD) measurements, and their catalytic performance for HAS was evaluated. The results showed that the total and C2+ alcohols selectivity of the catalyst after plasma treatment (TPR-MoP-Pla) were enhanced. The enhanced catalytic performance could be related to more dislocation defects and the synergistic effect between Mo0–2+ and Mo4+ valence species in the TPR-MoP-Pla catalyst. In addition, this work suggests that thermal plasma treatment can be used as a new preparation technique for the synthesis of materials with rich species.

Selective Hydrogenation of Acetylene over Pd-Mn/Al2O3 Catalysts

Novel bimetallic Pd-Mn/Al2O3 catalysts are designed by the decomposition of cyclopentadienylmanganese tricarbonyl (cymantrene) on reduced Pd/Al2O3 in an H2 atmosphere. The peculiarities of cymantrene decomposition on palladium and, thus, the formation of bimetallic Pd-Mn catalysts are studied. The catalysts are characterized by N2 adsorption, H2 pulse chemisorption, temperature-programmed desorption of hydrogen (TPD-H2), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The modified catalysts show the changed hydrogen chemisorption properties and the absence of weakly bonded hydrogen. Using an organomanganese precursor provides an uniform Mn distribution on the catalyst surface. Tested in hydrogenation of acetylene, the catalysts show both higher activity and selectivity to ethylene (20% higher) compared to the non-modified Pd/Al2O3 catalyst. The influence of the addition of Mn and temperature treatment on catalyst performance is studied. The optimal Mn content and treatment temperature are found. It is established that modification with Mn changes the route of acetylene hydrogenation from a consecutive scheme for Pd/Al2O3 to parallel one for the Pd-Mn samples. The reaction rate shows zero overall order by reagents for all tested catalysts.

Zn-Promoted Selective Gas-Phase Hydrogenation of Tertiary and Secondary C4 Alkynols over Supported Pd.

We have investigated the gas-phase (P = 1 atm; T = 373 K) hydrogenation of (tertiary alkynol) 2-methyl-3-butyn-2-ol (MBY) and (secondary) 3-butyn-2-ol (BY) over a series of carbon (C), non-reducible (Al2O3 and MgO), and reducible (CeO2 and ZnO) supported monometallic [Pd (0.6-1.2% wt) and Zn (1% wt)] and bimetallic Pd-Zn (Pd:Zn mol ratio = 95:5, 70:30, and 30:70) catalysts synthesized by deposition-precipitation and colloidal deposition. The catalysts have been characterized by H2 chemisorption, hydrogen temperature-programmed desorption (H2-TPD), specific surface area (SSA), X-ray photoelectron spectroscopy (XPS), and transmission (TEM) and scanning transmission electron microscopy (STEM) analyses. Reaction over these catalysts generated the target alkenol [2-methyl-3-buten-2-ol (MBE) and 3-buten-2-ol (BE)] through partial hydrogenation and alkanol [2-methyl-butan-2-ol (MBA) and 2-butanol (BA)]/ketone [2-butanone (BONE)] as a result of full hydrogenation and double-bond migration. The catalysts exhibit a similar Pd nanoparticle size (2.7 ± 0.3 nm) but a modified electronic character (based on XPS). Hydrogenation activity is linked to surface hydrogen (from H2 chemisorption and H2-TPD). An increase in H2:alkynol (from 1 → 10) results in enhanced alkynol consumption with a greater rate in the transformation of MBY (vs BY); H2:alkynol had negligible effect on product distribution. Reaction selectivity is insensitive to the Pd site electron density with a similar response (SMBE = 65 ± 9% and SBE = 70 ± 8%) over Pdδ- (on Al2O3 and MgO) and Pdδ+ (on C and CeO2). A Pd/ZnO catalyst delivered enhanced alkenol selectivity (SMBE = 90% and SBE = 96%) attributed to PdZn alloy phase formation (proved by XRD and XPS) but low activity, ascribed to metal encapsulation. A two-fold increase in the consumption rate was recorded for Pd-Zn/Al2O3 (30:70) versus Pd/ZnO with a similar alloy content (32 ± 4% from XPS), ascribed to a contribution due to spillover hydrogen (from H2-TPD) where high alkenol selectivity was maintained.

The Study of Reverse Water Gas Shift Reaction Activity over Different Interfaces: The Design of Cu-Plate ZnO Model Catalysts

CO2 hydrogenation to methanol is one of the main and valuable catalytic reactions applied on Cu/ZnO-based catalysts; the interface formed through Zn migration from ZnO support to the surface of Cu nanoparticle (ZnOx-Cu NP-ZnO) has been reported to account for methanol synthesis from CO2 hydrogenation. However, the accompanied reverse water gas shift (RWGS) reaction significantly decreases methanol selectivity and deactivates catalysts soon. Inhibition of RWGS is thus of great importance to afford high yield of methanol. The clear understanding of the reactivity of RWGS reaction on both the direct contact Cu-ZnO interface and ZnOx-Cu NP-ZnO interface is essential to reveal the low methanol selectivity in CO2 hydrogenation to methanol and look for efficient catalysts for RWGS reaction. Cu doped plate ZnO (ZnO:XCu) model catalysts were prepared through a hydrothermal method to simulate direct contact Cu-ZnO interface and plate ZnO supported 1 wt % Cu (1Cu/ZnO) catalyst was prepared by wet impregnation for comparison in RWGS reaction. Electron paramagnetic resonance (EPR), XRD, SEM, Raman, hydrogen temperature-programmed reduction (H2-TPR) and CO2 temperature-programmed desorption (CO2-TPD) were employed to characterize these catalysts. The characterization results confirmed that Cu incorporated into ZnO lattice and finally formed direct contact Cu-ZnO interface after H2 reduction. The catalytic performance revealed that direct contact Cu-ZnO interface displays inferior RWGS reaction reactivity at reaction temperature lower than 500 °C, compared with the ZnOx-Cu NP-ZnO interface; however, it is more stable at reaction temperature higher than 500 °C, enables ZnO:XCu model catalysts superior catalytic activity to that of 1Cu/ZnO. This finding will facilitate the designing of robust and efficient catalysts for both CO2 hydrogenation to methanol and RWGS reactions.

Enhancing CO2 Hydrogenation to Methane by Ni-Based Catalyst with V Species Using 3D-mesoporous KIT-6 as Support

Using renewable H2 for CO2 hydrogenation to methane not only achieves CO2 utilization, but also mitigates the greenhouse effect. In this work, several Ni-based catalysts with V species using 3D-mesoporous KIT-6 (Korea Advanced Institute of Science and Technology, KIT) as support were prepared at different contents of NiO and V2O5. Small Ni nanoparticles with high dispersibility on 20Ni-0.5V/KIT-6 were identified by X-ray diffraction (XRD), TEM and hydrogen temperature-programmed desorption (H2-TPD) analysis, which promoted the production of more Ni active sites for enhancing catalytic activity for CO2 methanation. Moreover, TEM and hydrogen temperature-programmed reduction (H2-TPR) characterizations confirmed that a proper amount of Ni and V species was favorable to preserve the 3D-mesoporous structure and strengthen the interaction between active Ni and KIT-6. The synergistic effect between Ni and V could strengthen surface basicity to elevate the ability of CO2 activity on the 20Ni-0.5V/KIT-6. In addition, a strong interaction with the 3D-mesoporous structure allowed active Ni to be firmly anchored onto the catalyst surface, which was accountable for improving catalytic activity and stability. These results revealed that 20Ni-0.5V/KIT-6 was a catalyst with superior catalytic activity and stability, which was considered as a promising candidate for CO2 hydrogenation to methane.

INFLUENCE OF MANGANESE ON FORMATION OF ACTIVE PHASE OF COBALT CATALYST OF HYDROCARBON SYNTHESIS

The active phase and catalytic properties of cobalt catalysts of Fischer-Tropsch synthesis promoted with manganese and prepared by impregnation were studied. KSKG silica gel having a monodisperse structure with an average pore diameter of 12–16 nm was used as a support. The cobalt content in the obtained samples was 20.8-21.8 wt.%, manganese content was 0.5–2 wt.%. The structural characteristics of the catalysts were investigated by X-ray diffraction, transmission electron microscopy, temperature-programmed reduction and temperature-programmed hydrogen desorption. The catalytic activity and selectivity of the samples in the process of hydrocarbon synthesis were researched in the flow mode at a pressure of 0.1 MPa, at a Gas Hourly Space Velocity (GHSV) of 100 h–1, at the temperatures of 150–220 °C and a ratio of CO to hydrogen in synthesis gas of 2:1. Preliminary reduction of catalysts was carried out with hydrogen at a temperature of 400 °C. In the composition of the studied samples with manganese the formation of solid solutions of metals such as xCo3O4–(1–x)Mn3O4 was confirmed. It is shown that the reduction process of Co3O4 is determined by the composition and structure of solid solutions of components that are hard-to-recover compounds. The features of the promoting action of manganese depending on the concentration are determined. The introduction of 0.5–2 wt.% manganese allows to regulate the composition and microstructure of cobalt oxide compounds, the properties of metallic Co, increases the catalytic characteristics: activity, selectivity for C5+ and reduces the yield of methane. It is shown how, depending on the content of the metal additive, the manifestations of the structural (at a concentration of 0–1 wt.%) or electronic (at a concentration of 2 wt.%) promoting action of manganese increase. The optimum concentration of manganese is 1 wt.%. The catalyst is characterized by the minimum average size of crystallites, the highest value of the specific surface of cobalt metal and the maximum catalytic indicators.