H2 Temperature-programmed Desorption Research Articles

Biogas dry reforming over Li–Ni–Al LDH-derived catalysts

Biogas dry reforming or dry reforming of methane (DRM) is an alternative to produce hydrogen, in the context of development of sustainable routes for energy production, since this route uses CH4 and CO2, two greenhouse gases as reactants. However, the deactivation of catalysts due to carbon deposition and sintering is the main drawback of this reaction. In this work, with the aim of minimizing carbon formation and sintering during DRM, the effect of lithium as a promoter in catalysts Ni–Al derived from layered double hydroxides was investigated. The catalysts were prepared by co-precipitation and characterized by different techniques: BET surface area (SBET), X-ray diffraction (XRD), temperature-programmed reduction (TPR), CO2 and H2 temperature-programmed desorption (CO2-TPD and H2-TPD), Scanning Electron Microscopy (SEM-EDS), temperature-programmed oxidation (TPO). The catalytic tests were carried out in a fixed bed reactor using a synthetic biogas (60% CH4 and 40% CO2) in the temperature range of 500–750 °C. The incorporation of Li into the Ni–Al-LDH changed the reducibility and basicity of the catalysts. The Li2 sample containing an intermediary amount of Li (5 wt%) showed the highest reduction temperature and highest density of basic sites, which resulted in the smallest Ni crystallite size before and after the reactions. As a result, this catalyst presented the greater resistance to sintering and a lower rate of carbon produced. For the reaction carried out at 700 °C, only the Li2 catalyst remaining active during the test and reaching a maximum of 80% and a final CH4 conversion of 54% after 480 min of reaction, whereas CO2 conversion was higher than 90%. All other samples deactivated at different rates due to carbon deposition and sintering.

Theoretical study of hydrogen desorption on the Ni(100) surface through simulated temperature programmed desorption spectra

Nickel has been widely used as heterogeneous catalysts in important reactions such as dehydrogenation and steam reforming, where the desorption of H2 molecules is one of the key steps. Herein, based on density functional theory calculations, we have simulated the temperature programmed desorption (TPD) spectra of hydrogen (H) on the Ni(100) surface using the mean-field approximation and a new HH dimer desorption method. Zero-point energy corrections are also considered. It is found that the centered-peaks of TPD obtained from simulations are in good agreement with the previous experimental results. However, the centered-peak position moves in an opposite direction to the experiments as atomic hydrogen coverage increases. We have systematically investigated the effects of the interaction between adsorbed H atoms and the diffusion of H atoms on the peak shifts, and found that they are not responsible for the experimentally observed leftward shift of the TPD peak. We then propose and confirm that the presence of subsurface H atoms plays a key role in the leftward peak shift. This work refines the interpretation of H2 TPD spectra and contributes to the understanding of microscopic behaviors of H atoms on the Ni(100) surface.

The discrepancy of NH3 oxidation mechanism between SAPO-34 and Cu/SAPO-34.

The difference of NH3 oxidation mechanism over SAPO-34 and Cu-SAPO-34 was studied. XRD (X-ray diffraction), SEM (scanning electron microscopy) and H2-TPR (H2-temperature programmed desorption) were conducted to estimate the Cu species distribution. The quantity of individual Cu2+ ions escalated with the elevation of silicon content in the Cu/SAPO-34 catalysts, leading to an enhancement in the activity of the NH3-SCR (ammonia-selective catalytic reduction) process. This augmentation in activity can be attributed to the increased presence of isolated Cu2+ species, which are pivotal in facilitating the catalytic reaction. In addition, the kinetic test of NH3 oxidation indicated that the CuO species were the active sites for NH3 oxidation. Specifically, the strong structural Brønsted acid sites were the NH3 oxidation active sites over the SAPO-34 support, and the NH3 reacted with the O2 on the Brønsted acid sites to produce the NO mainly. While the NH3 oxidation mechanism over Cu/SAPO-34 consisted of two steps: firstly, NH3 reacted with O2 on CuO sites or residual Brønsted acid sites to form NO as the product; subsequently, the generated NO was reduced by NH3 into N2 on isolated Cu2+ sites. Simultaneously, the isolated Cu2+ sites might demonstrate a significant function in the NH3 oxidation process to form N2. The identification of active sites and corresponding mechanism could deepen the understanding of excellent performance of NH3-SCR over the Cu/SAPO-34 catalyst at high temperature.

Influence of Carbonization Conditions on Structural and Surface Properties of K-Doped Mo2C Catalysts for the Synthesis of Methyl Mercaptan from CO/H2/H2S.

The cooperative transition of sulfur-containing pollutants of H2S/CO/H2 to the high-value chemical methyl mercaptan (CH3SH) is catalyzed by Mo-based catalysts and has good application prospects. Herein, a series of Al2O3-supported molybdenum carbide catalysts with K doping (denoted herein as K-Mo2C/Al2O3) are fabricated by the impregnation method, with the carbonization process occurring under different atmospheres and different temperatures between 400 and 600 °C. The CH4-K-Mo2C/Al2O3 catalyst carbonized by CH4/H2 at 500 °C displays unprecedented performance in the synthesis of CH3SH from CO/H2S/H2, with 66.1% selectivity and a 0.2990 g·gcat-1·h-1 formation rate of CH3SH at 325 °C. H2 temperature-programmed reduction, temperature-programmed desorption, X-ray diffraction and Raman and BET analyses reveal that the CH4-K-Mo2C/Al2O3 catalyst contains more Mo coordinatively unsaturated surface sites that are responsible for promoting the adsorption of reactants and the desorption of intermediate products, thereby improving the selectivity towards and production of CH3SH. This study systematically investigates the effects of catalyst carbonization and passivation conditions on catalyst activity, conclusively demonstrating that Mo2C-based catalyst systems can be highly selective for producing CH3SH from CO/H2S/H2.

Effect of MgFe-LDH with Reduction Pretreatment on the Catalytic Performance in Syngas to Light Olefins

MgFe-layered double hydroxides (LDH) were widely used as catalysts for Fischer–Tropsch synthesis to produce light olefins, in which the state of Fe-species may affect the resulting catalytic active sites. Herein, the typical MgFe-LDH was hydrothermally synthesized and the obtained MgFe-LDH was pretreated with H2 at different temperatures to reveal the effects of the state of Fe-species on the catalytic performance in Fischer–Tropsch synthesis. MgFe-LDH materials were characterized by X-ray diffraction (XRD), N2 adsorption–desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), H2 temperature-programmed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS). It was found that a MgO-FeO solid solution would be formed with the increase of the reduction temperature, which made the electrons transfer from Mg atoms to Fe atoms and strengthened the adsorption of CO. The pre-reduced treatment toward Mg-Fe-LDH enabled the FeCx active sites to be easily formed in situ during the reaction process, leading to the high conversion of CO. CO2 temperature-programmed desorption (CO2-TPD) and H2 temperature-programmed desorption (H2-TPD) analysis confirmed that the surface basicity of the catalysts was increased and the hydrogenation capacity was weakened, the secondary hydrogenation of the olefins was inhibited, and therefore as were the enhancement of O/P in the product and the high selectivity of light olefins (42.7%).

Boosting Hydrogen Oxidation Kinetics by Promoting Interfacial Water Adsorption on d-p Hybridized Ru Catalysts

The search for highly efficient and cost-effective electrocatalysts for hydrogen oxidation reaction (HOR) under alkaline electrolytes is essential for the commercial application of anion exchange membrane fuel cells. However, the kinetics of HOR in an alkaline media is much slower than that in an acidic electrolyte, which usually results in orders of magnitude decrease in the catalytic performance. Herein, we report the synthesis of d-p orbital hybridized Ru catalysts through Sn/Ga doping. Density functional theory (DFT) calculations and experimental results including H2-temperature programmed desorption (H2-TPD) and in situ Raman spectra unveil that the electronic structure modification of Ru derived from the unconventional d-p hybridization could lead to the promoted interfacial water adsorption ability and optimized hydrogen adsorption free energy during the alkaline HOR process. As expected, the d-p hybridized Ru catalyst shows much decreased formation energy of water, which contributes to the changed potential-determining step (PDS) and remarkable HOR activity with the mass activity up to 1790 mA mgRu–1. This work not only illustrates the key role of interfacial water adsorption ability but also provides a strategy for rationally designing advanced electrocatalysts for alkaline HOR.

Co-Ni bimetallic supported on mullite as a promising catalyst for biogas dry reforming toward hydrogen production

Dry reforming of methane, in which harmful greenhouse gases convert to syngas, is one of the most important approaches to reducing concerns about global warming and increasing greenhouse gases. It was well found that support has a key role in the catalytic performance of heterogeneous catalysts in all aspects of chemistry. In this study, the effect of mullite(3Al2O3·2SiO2) ceramics as a support for the immobilization of Ni and Co to prepare bimetallic catalyst was explored in dry reforming of methane (DRM) at a temperature range of 650–800°C and gas hour space velocity (GHSV) equal to 15000 ml g⁻¹ h⁻¹. To evaluate the synergetic effect of the Ni-Co alloy, the diverse range of Ni/Co mass ratios (1:0, 2:1, 1:1, 1:2, 0:1) were prepared via the co-impregnation method. The synthesized materials were characterized through X-ray powder diffraction (XRD), N2 adsorption/desorption, transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), dot mapping analysis, Dispersive X-ray Spectroscopy (EDS), Dynamic light scattering (DLS), temperature-programmed reduction analysis (H2-TPR), H2 temperature programmed desorption (H2-TPD), and thermogravimetric analysis (TGA). Based on findings, the mullite support has the high potential to act as appropriate support to immobilize metal particles with good distribution, which is beneficial for BR, especially in terms of coke and sintering resistivity. Among synthesized catalysts, 10%Ni-10%Co/mullite showed the highest CH4, CO2 conversions, and H2 yield at 800°C.

Dry Reforming of Methane on Ni/Nanorod-CeO2 Catalysts Prepared by One-Pot Hydrothermal Synthesis: The Effect of Ni Content on Structure, Activity, and Stability

The nanorod morphology of the CeO2 support has been recognized as more beneficial than other morphologies for catalytic activity in the dry reforming of methane. Ni/nanorod-CeO2 catalysts with different Ni contents were prepared by one-pot hydrothermal synthesis. Samples were characterized by X-ray diffraction (XRD), H2-temperature-programmed reduction (H2-TPR), H2-temperature-programmed desorption (H2-TPD), field emission scanning electron microscopy/energy dispersive spectroscopy (FE-SEM/EDS), Brunauer–Emmet–Teller (BET) and Barrett–Joyner–Halenda (BHJ) analysis. The effect of Ni content on the size and the intrinsic strain of ceria was analyzed by the Size–Strain plot and Williamson–Hall plot of XRD data. The average Ni particle size and Ni dispersion were determined by H2-TPD. XRD and H2-TPR analysis revealed a strong Ni–support interaction that limited nickel sintering. The activity for the dry reforming of methane was tested with the stoichiometric mixture CO2:CH4:N2:He = 20:20:20:140, gas hourly space velocity (GHSV) = 300 L g−1 h−1, and temperatures in the range of 545–800 °C. The turnover frequency (TOF) value increased linearly with the average Ni particle size in the range of 5.5–33 nm, suggesting the structure sensitivity of the reaction. Samples with Ni loading of 4–12 wt.% showed high H2/CO selectivity and stability over time on stream, whereas the sample with a Ni loading of 2 wt.% was less selective and underwent rapid deactivation. Only a small amount of nanotubular carbon was observed by FE-SEM after the time-on-stream experiment. Deactivation of the low-Ni-content sample is ascribed to the easier oxidation of the small Ni particles.

Temperature programmed desorption comparison of lunar regolith to lunar regolith simulants LMS-1 and LHS-1

Water and molecular hydrogen evolution from Apollo sample 14163 and lunar regolith simulants LMS-1, a mare simulant, and LHS-1, a highlands simulant, were examined using Temperature Programmed Desorption (TPD) in ultra-high vacuum. LMS-1, LHS-1, and Apollo 14163 released water upon heating, whereas only the Apollo sample directly released measurable quantities of molecular hydrogen. The resulting H2O and H2 TPD curves were fit using a model which considers desorption at the vacuum grain interface, transport in the void space between grain-grain boundaries, molecule formation via recombination reactions and sub-surface diffusion. The model yielded a most probable H2O formation and desorption effective activation energy of ∼150 kJmol−1 for all samples. The probability distribution widths of the effective activation energies were ∼100–400, ∼100–350, and ∼100–300 kJmol−1 for LMS-1, LHS-1, and Apollo 14163, respectively. In addition to having the narrowest energy distribution width, the Apollo sample released the least amount to water (103 ppm) relative to LMS-1 (176 ppm) and LHS-1 (195 ppm). Since essentially no molecular hydrogen was observed from the simulants, the results indicate that LMS-1 and LHS-1 display water surface formation, binding, and transport interactions similar to actual regolith but not the desorption chemistry associated with the implanted hydrogen from the solar wind. Overall, these terrestrial surrogates are useful for understanding the surface and interface interactions of lunar regolith grains, which are largely dominated by the terminal hydroxyl sites under both solar wind bombardment and terrestrial preparation conditions.

One pot sol-gel synthesis of Pt−Ni/TiO2 with high CO2 methanation catalytic activity at low temperature

In this work, 2 wt%Pt/TiO2, 20 wt%Ni/TiO2 monometallic catalysts and xwt%Pt−20 wt%Ni/TiO2 (x = 1, 2 and 4 wt%) bimetallic catalysts were synthesized by one-pot sol-gel method for CO2 methanation reaction. All bimetallic catalysts revealed higher CO2 conversion than both monometallic catalysts. The 2 wt%Pt−20 wt%Ni/TiO2 catalyst exhibited the highest percentage of CO2 conversion at low reaction temperature, with almost 100% CH4 selectivity and high stability during 72 h time on stream. The effect of Pt co-doped with Ni to bimetallic formed on the catalyst properties was studied using several techniques, including X-ray diffraction, N2 adsorption-desorption, Raman spectroscopy, transmission electron microscopy, field emission scanning electron microscopy, H2 temperature-programmed desorption, H2 temperature-programmed reduction, CO2 temperature-programmed desorption and X-ray absorption spectroscopy (both ex-situ and in-situ experiments). The results showed that Pt was dispersed on the catalyst surface in the form of platinum oxide, while Ni was both incorporated into the TiO2 lattice with the excess amount from saturated level being dispersed on the catalyst surface. The results from XAS evidenced that some electrons movement from Ni to Pt occurred. This electronic property changing can tune the interaction between Ni and TiO2 support with appropriate strength and then resulting in higher reducibility of the catalyst and higher dispersion of Ni species. Furthermore, the electron-rich Pt site on the catalyst surface favored to adsorb CO from CO2 dissociation and further activated adsorbed CO to interact with nearby hydrogen atoms to form CH4 leading to high CO2 methanation activity at low temperature.

Deep Adsorption Desulfurization of Fluid Catalytic Cracking Light Gasoline on NiO/ZnO-TiO2 Adsorbents with a High Breakthrough Sulfur Capacity.

Two kinds of NiO/ZnO-TiO2 adsorbents were prepared by equal volume impregnation (NiO/ZnO-TiO2-1) and kneading (NiO/ZnO-TiO2-2) methods. The adsorbents were characterized by X-ray diffraction, mercury intrusion porosimetry, scanning electron microscopy, energy dispersive X-ray spectroscopy, H2 temperature-programmed reduction, and H2 temperature-programmed desorption. It was found that NiO/ZnO-TiO2-2 had a smaller average pore diameter and a larger specific surface area as well as a more uniform distribution of the nickel element. Additionally, more Ni0 active sites together with a stronger interaction between the active component and the support were detected on the surface of NiO/ZnO-TiO2-2, which was beneficial to the inhibition of olefin saturation during desulfurization. The desulfurization performance of the adsorbents was investigated in a fixed bed reactor with fluid catalytic cracking light gasoline as a feed oil. The evaluation results confirmed NiO/ZnO-TiO2-2 with a better desulfurization performance with less olefin saturation. It could reduce the total sulfur content from 300 ppmw to less than 5 ppmw, and the breakthrough time and breakthrough sulfur capacity were 91 h and 6.71% (67.1 mg S/g adsorbent), respectively.

Effect of the Support Synthetic Method on the Activity of Ni/CeZrPr Mixed Oxide in the Co-Methanation of CO2/CO Mixtures for Application in Power-to-Gas with Co-Electrolysis

Synthetic natural gas (SNG) is an efficient option for transforming renewable energy into carbon-neutral fuels while using a plug-and-play infrastructure, supporting the transition to renewable energy, paving the way for a hydrogen-based economy. Captured CO2 can be processed with water through high-temperature co-electrolysis, where reduction to CO and H2 production by water splitting occurs. The outlet gas, composed of CO2, CO, H2, and small amounts of CH4, can be used to produce SNG by methanation of CO and CO2 with hydrogen. Among the parameters influencing the methanation reactions, the characteristics of the support and its interaction with the metallic active phase, usually Ni, are of crucial importance and can be tuned by the synthesis of the support. For this reason, three different synthetic methods, namely, pseudo sol–gel, coprecipitation, and colloidal combustion, were applied to the synthesis of a Ce/Zr/Pr oxide. The supports were fully characterized by nitrogen physisorption, X-ray diffraction (XRD), scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS), temperature-programmed reduction (TPR), and H2 temperature-programmed desorption (H2-TPD) before and after impregnation with 10 wt % Ni. The coprecipitated catalyst exhibited the best performances when subjected to CO2/CO co-methanation and typical post-co-electrolysis mixture, thanks to a combination of different characteristics such as high surface area and mesoporosity, which allowed good Ni dispersion and surface area, high support metal interaction, and reducibility. Finally, the effect of Pr seemed to be beneficial, increasing the methane yield at low temperatures.

CO and H2 adsorption on Au-Ni bimetallic surfaces: a combined experimental and DFT theoretical study

Au-Ni bimetallic thin films were grown on refractory metal substrates. CO and H2 adsorption on Au-Ni bimetallic surfaces have been studied by a combination of in situ polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), temperature-programmed desorption (TPD), and density functional theory (DFT) calculations. It is found CO desorption peak shifts from 413 K on pure Ni surfaces to 293 K on the isolated Ni atoms formed by alloying with Au atoms. The sharp decrease of CO desorption temperature on Au-Ni surfaces with increasing Au coverage is caused by the change of the favored CO adsorption sites from bridge/hollow sites on pure Ni surfaces to Ni top sites on Au-Ni bimetallic surfaces. In situ PM-IRRAS shows two CO adsorption bands on Au sites at 2119 cm−1 and 2103 cm−1 on Au-Ni surfaces at 80 K, which are due to CO bound on under-coordinated Au atoms and electron negatively charged Au sites modified with nearby Ni atoms, respectively. Even with the Au-Ni surface temperature at as low as 100 K, CO adsorption induced Ni surface segregation has been observed by in situ PM-IRRAS. Furthermore, DFT calculation results discover the adsorption energy of CO on Ni top sites continues to decrease with increasing Au coverage due to the geometric ensemble effect and the lowered d-band center after Ni alloying with Au. H2 desorption temperature decreases from 363 K on pure Ni thin films to 302 K with increasing Au coverage to 0.6 ML. A new H2 peak appears at around 170 K on the Au-Ni surfaces with Au coverages between 0.6 ML and 0.9 ML. This new H2 TPD peak is assigned to H2 desorption from the totally isolated Ni sites. With Au coverage above 1.5 ML, there is no any H2 desorption detected. The combined surface science studies and DFT calculations provide new insights into the surface structure-activity correlation of Ni-base bimetallic surface alloys.

High-Performance Ru 2 P Anodic Catalyst for Alkaline Polymer Electrolyte Fuel Cells

High-Performance Ru ₂ P Anodic Catalyst for Alkaline Polymer Electrolyte Fuel Cells

Enhanced CO2 methanation activity over Ni/CeO2 catalyst by one-pot method

Abstract Carbon dioxide hydrogenation for value-added chemicals has been regarded as a promising way for CO2 utilization. This paper describes the preparation of Ni/CeO2 catalysts derived from Ce-MOF precursor by impregnation or one-pot method and their application in carbon dioxide methanation. Various techniques were employed to characterize the prepared catalysts, including N2 adsorption–desorption, X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (SEM), H2-temperature programmed reduction (H2-TPR), H2-temperature programmed desorption (H2-TPD) and CO2-temperature programmed desorption (CO2-TPD). The results showed that compared with commercial CeO2 and CeO2 prepared by precipitation, CeO2 derived from Ce-MOF exhibited more oxygen vacancies and lower temperature reducibility, making it more beneficial for the adsorption and activation of CO2. Consequently, nickel supported on rod-shaped CeO2 derived from Ce-MOF exhibited higher CO2 conversion and methane selectivity at low temperatures. Furthermore, the Ni/CeO2−M-1 catalysts prepared by one-pot method showed superior activity since nickel could be partially incorporated into ceria lattice, leading to the formation of Ce1-xNixO2-y solid solutions and oxygen vacancies. The effect of nickel loading on the properties of the catalysts by one-pot method was also investigated, and the optimum Ni loading was 15 wt.% owing to the maximum number of oxygen vacancies being reached.

Combustion-impregnation preparation of Ni/SiO2 catalyst with improved low-temperature activity for CO2 methanation

Exploiting Ni-based catalysts with excellent low-temperature activity is significant for CO2 methanation, which is a promising route to CO2 utilization. In this work, a facile combustion-impregnation method was developed to prepare the SiO2 supported Ni catalysts. Small Ni particles (around 6 nm) and massive Ni–SiO2 interface could be obtained due to the “combustion” process. The H2-temperature programmed desorption (H2-TPD) revealed the existence of Ni–SiO2 interface and confirmed the high Ni dispersion obtained by this method, which were vital for the activation of reactant. Moreover, more medium basic sites which were beneficial for the CO2 activation could also be created. In comparison with the reference Ni/SiO2 catalyst prepared by the conventional impregnation method, much higher CO2 conversion (66.9%) and more superior selectivity to CH4 (94.1%) were achieved with the Ni/SiO2-Gly catalyst at 350 °C. Additionally, it was also found that glucose, citric acid and glycine were all effective fuels for this combustion-impregnation method, and the as-prepared catalysts all exhibited greatly improved low-temperature activity. Therefore, this work represents an important step toward developing Ni-based catalysts for CO2 methanation by a promising wide-used method.

Improved performance of Ni/Al2O3 catalyst deriving from the hydrotalcite precursor synthesized on Al2O3 support for dry reforming of methane

Exploiting Ni-based catalysts with excellent catalytic activity and anti-coking ability is significant for dry reforming of CH4 with CO2 (DRM) which is a promising route to CO2 utilization. In this work, the Ni/Al2O3 catalyst with hydrotalcite precursor (NiAl-LDH) was synthesized by a facile in-situ growth method. And the effect of the NiAl-LDH structure on the catalytic activity and anti-coking ability of Ni/Al2O3 catalyst was revealed. The H2-temperature programmed desorption (H2-TPD) revealed that better Ni dispersion and more Ni–Al2O3 interface could be obtained by the NiAl-LDH precursor, which were vital for the activation of CH4 and CO2. Moreover, the NiAl-LDH precursor with non-LDH phase or turbostratic structure was also created by insufficient or extra amount of urea, and the obtained catalysts exhibited a poor catalytic stability, further confirming the importance of the LDH structure. In comparison with the Ni-IMP catalyst prepared by the conventional impregnation method, the CH4 conversion increased by 16% and the carbon deposition decreased by 75% over Ni-6 catalyst with well-organized LDH precursor under the same reaction conditions. Hence, this work represents an important step toward developing Ni-based catalysts with excellent catalytic activity and anti-coking ability for DRM with the LDH precursor.

Direct Conversion of Syngas to Light Olefins through Fischer-Tropsch Synthesis over Fe-Zr Catalysts Modified with Sodium.

Fe–Zr–Na catalysts synthesized by coprecipitation and impregnation methods were implemented to investigate the promoting effects of Na and Zr on the iron-based catalyst for high-temperature Fischer–Tropsch synthesis (HTFT). The catalysts were characterized by Ar adsorption–desorption, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, CO temperature-programmed desorption, H2 temperature-programmed desorption, X-ray photoelectron spectroscopy, and Mössbauer spectroscopy (MES). The results indicated that Na changed the active sites on the catalyst surface for the CO and hydrogen adsorption, owing to the electron migration from Na to Fe atoms, which resulted in an enhanced CO dissociative adsorption and a decrease in hydrogen adsorption on the metallic Fe surface. The decreased H/C ratio on the catalyst surface accounted for the increased chain propagation and weakened hydrogenation of light olefins. Besides, Na could also facilitate the carbonization of catalysts and protect the iron carbide against oxidation, which provides more active sites for HTFT reaction and is beneficial to the C–C coupling. Zr could decrease the hematite crystallite size and stabilize the active phase to improve the HTFT activity. At an optimal Na loading of 1.0 wt %, the Fe–Zr–1.0Na catalyst exhibited the highest light olefin selectivity of 35.8% in the hydrocarbon distribution at a CO conversion of 95.2%.

Inverse ZnO/Cu catalysts for methanol synthesis from CO2 hydrogenation

A series of inverse ZnO/Cu catalysts were prepared with varied Zn/Cu ratios using a microemulsion method. The catalysts were tested for CO2 hydrogenation to methanol and the structure was characterized by nitrogen physisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Transmission electron microscopy (TEM), Scanning electron microscope (SEM), H2 temperature-programmed reduction (H2-TPR) and H2 temperature-programmed desorption (H2-TPD). On the inverse samples, less amount of highly dispersed Cu was observed than that of the conventional Cu/ZnO catalysts. Thus, the inverse ZnO/Cu catalysts showed a lower CO selectivity and a higher methanol selectivity. CuZn alloy was formed in the samples, in which ZnO/Cu(4:6) had the most amount of the CuZn alloy. A linear relationship between the methanol yield and the CuZn alloy content can be found for the ZnO/Cu catalysts. Among all the catalysts, ZnO/Cu(4:6) exhibited the highest CH3OH yield (2.8 mmol g−1 h−1) at 2.0 MPa and 250 °C, much higher than the conventional Cu/ZnO catalyst with the same composition. Moreover, microemulsion method is a very effective method to tune particle size of the catalysts.

Role of ZnNb2O6 in ZnO-promoted amorphous-Nb2O5 supported Ru catalyst for the partial hydrogenation of benzene

Ruthenium catalysts supported on zinc-promoted amorphous-niobium mixed oxides were prepared, characterized, and studied in the additive-free partial hydrogenation of benzene reaction. The amorphous matrix of Nb2O5 was responsible for a highly active Ru/Nb2O5 catalyst, although less selective than those containing zinc. The ZnO-containing supports were prepared by wet impregnation technique, followed by incipient wetness of ruthenium chloride salt. The catalysts were characterized by textural analysis, X-ray fluorescence, X-ray diffraction, H2 chemisorption, temperature-programmed reduction (TPR), Scanning electron microscopy, H2 temperature-programmed desorption, and X-ray photoelectron spectroscopy (XPS) of the calcined-reduced samples. Chlorine retention was observed on zinc-containing samples. An unexpected ZnNb2O6 oxide phase, ascribed to a selectivity increase with less activity loss, was obtained for the supports at lower temperatures than those related on the literature. A very complex electronic environment of Ru- and Zn-containing species interactions was observed by TPR. The presence of surface-reduced (Ru0) and partially reduced (Ruδ+) Ru species observed by XPS justified well, respectively, the activity and selectivity achieved with every catalyst. The addition of water as a solvent resulted in very constant yield to cyclohexene, as expected, despite activity diminution due to low solubility of the reactants.