Rate Of CO Hydrogenation Research Articles

A synergetic effect between a single Cu site and S vacancy on an MoS2 basal plane for methanol synthesis from syngas

Compared to MoS2(001), the synergetic effect between the single Cu site and S vacancy on Cu/MoS2(001) destabilizes O, which not only increases the CO hydrogenation rate by 5 orders of magnitude, but leads to the selectivity switch from CH4 to CH3OH.

Tailoring Rh content on dendritic fibrous silica alumina catalyst for enhanced CO2 capture in catalytic CO2 methanation

Dendritic fibrous X%Rh/FSA catalysts were synthesized by the microwave-assisted microemulsion and wetness impregnation approaches. Catalytic CO2 methanation was performed at temperature ranging of 150‒500 °C and atmospheric pressure with stoichiometric feed composition. FESEM and TEM micrographs confirmed the spherical bicontinuous concentric lamellar morphology of FSA offering high accessibility of capturing CO2 to the active sites, thus promotion of heterogenous catalysis activity. H2-TPR and pyrrole adsorbed IR spectroscopy results reveals that the metal-support interaction and degree of basicity strength were enormously enhanced with the increasing Rh content. The 1%Rh appeared to be the optimal loading with respect to the CO2 conversion and CH4 formation rate as a function of temperature, accredited to its medium basicity strength and fibrous morphology. The in situ FTIR analyses showed that medium basic sites promoted the desired carbonate species that readily participate into hydrogenation compared to strong basic sites. In addition, CH4/CO2 ratio indicates that the rate of CO hydrogenation was superior to that of RWGS over Rh/FSA catalysts. The absence of graphitic carbon for all spent Rh/FSA catalysts in post-characterization analyses suggests that their excellent catalytic performance could be assigned to the preservation of most active sites owing to enhanced CO2 adsorption on catalyst surface which effectively remove amorphous carbon deposits via CO2 gasification process.

Preparation of Purified Hydrogen by Selective Hydrogenation of Carbon Monoxide in a Mixture of Steam Reforming Products of Organic Substrates Using a Membrane Catalytic Reactor

The scientific basis has been developed for the production of purified hydrogen via the hydrogenation of CO formed by the steam reforming of fermentation products in a porous Ni(Al)–Co converter made by self-propagating high-temperature synthesis. It has been shown that the rate of CO hydrogenation in catalytic channels of the converter is higher by a factor of 3–3.5 than the rate achieved in a flow reactor with a fixed bed of a granular catalyst of the same composition. If the steam reforming processes with an H2O/organic substrate ratio of ~15–20 are self-consistent with the subsequent hydrogenation of carbon monoxide by the “intrinsic” hydrogen, the carbon monoxide conversion per pass at 300°C is 97.5% with a residual CO content in the gas of ≤0.1%. The approach considered in the paper is promising for producing hydrogen as a fuel for medium-temperature fuel cells.

Correlating Fischer-Tropsch activity to Ru nanoparticle surface structure as probed by high-energy X-ray diffraction.

Synchrotron X-ray diffraction coupled to atomic pair distribution function analysis and Reverse Monte Carlo simulations is used to determine the atomic-scale structure of Ru nanoparticle catalysts for the Fischer-Tropsch reaction. The rate of CO hydrogenation strongly correlates with the abundance of surface atoms with coordination numbers of 10 and 11. DFT calculations confirm that CO dissociation proceeds with a low barrier on these Ru surface atom ensembles.

Effects of Cu–ZnO Content on Reaction Rate for Direct Synthesis of DME from Syngas with Bifunctional Cu–ZnO/γ-Al2O3 Catalyst

The effects of Cu–ZnO content on the performance of bifunctional Cu–ZnO/γ-Al2O3 catalysts for dimethyl ether (DME) synthesis from syngas were investigated by varying the weight ratios of Cu–ZnO/γ-Al2O3 prepared by the coprecipitation of Cu–ZnO in a slurry of γ-Al2O3. A higher rate of DME production with CO conversion of 47.6 % and DME selectivity of 61.1 % was observed with the bifunctional catalyst at an optimal weight ratio of CuO/γ-Al2O3 of two, providing a higher surface area of metallic copper and an abundance of weak acid sites. The number of acidic sites on solid-acid γ-Al2O3 is a more crucial factor to enhance DME yield, due to the faster dehydration rate of methanol to DME than that of CO hydrogenation to methanol. Although the first step of methanol synthesis on active copper sites is a rate-limiting step with a low equilibrium value, the second step of the dehydration of methanol to DME on acid sites adjusts the overall rate by enhancing the forward reaction rate of CO hydrogenation to methanol with a simultaneous formation of surplus hydrogen by a water–gas shift reaction. Therefore, the proper design of a high surface area of metallic copper with larger acid sites on the bifunctional CuO–ZnO/γ-Al2O3 catalysts at an optimal ratio, produced by adjusting the weight ratio of CuO/γ-Al2O3, is an important factor for improved catalytic performance.

Fischer–Tropsch synthesis: Effect of promoter type on alumina-supported Mo carbide catalysts

Molybdenum carbide catalysts promoted with K, Na, Co, and Ce have been synthesized by temperature-programmed carburization using a mixture of H 2/C 3H 8 and evaluated for the Fischer–Tropsch synthesis. Both α- and β-Mo carbide catalysts were produced during carburization via the formation of oxycarbide intermediate phase. The two-stage Mo carbide synthesis appeared to be characterized by a compensation effect and isokinetic relationship for both promoted and undoped catalysts suggesting that the solid state transformation mechanism was similar across the promoters. The catalysts possessed relatively high BET area (177–210 m 2 g cat −1) with finely dispersed Mo carbide particles (ca. 10 nm) on the alumina support. The presence of weak and strong acid–base sites was also confirmed by NH 3 and CO 2-TPD runs. CO hydrogenation rate increased with H 2 composition reaching optimal activity at y H 2 between 0.67 and 0.75. FT activity improved with promoter addition in the order; K–MoC 1− x /Al 2O 3 > Na–MoC 1− x /Al 2O 3 > Ce–MoC 1− x /Al 2O 3 > Co–MoC 1− x /Al 2O 3 > MoC 1− x /Al 2O 3 while chain growth probability varied with feed composition and was enhanced by all promoters. The reaction rate data were adequately described by an Eley–Rideal model.

Modeling of the Kinetics for Methanol Synthesis using Cu/ZnO/Al2O3/ZrO2 Catalyst: Influence of Carbon Dioxide during Hydrogenation

A kinetic model for methanol (MeOH) synthesis over Cu/ZnO/Al2O3/ZrO2 catalyst has been developed and selected to evaluate the effect of carbon dioxide on the reaction rates due to its high activity and stability. Detailed kinetic mechanism, on the basis of different sites on Cu for the adsorption of carbon monoxide and carbon dioxide, is applied, and the water−gas shift (WGS) reaction is included in order to provide the relationship between the hydrogenations of carbon monoxide and carbon dioxide. Parameter estimation results show that, among 48 reaction rates from different combinations of rate determining steps (RDSs) in each reaction, the surface reaction of a methoxy species, the hydrogenation of a formate intermediate HCO2, and the formation of a formate intermediate are the RDS for CO and CO2 hydrogenations and the WGS reaction, respectively. It is shown that the CO2 hydrogenation rate is much lower than the CO hydrogenation rate, and this affects the methanol production rate. However, carbon dioxide decreases the WGS reaction rate, which prevents methanol from converting to dimethyl ether, a byproduct. In such a way, a small fraction of carbon dioxide accelerates the production of methanol indirectly within a limited range, showing a threshold value of the CO2 fraction for the maximum methanol synthesis.

Effects of Impregnation Solvents on Catalytic Performance of Co-Ru-ZrO2/γ-Al2O3 Catalyst for Fischer-Tropsch Synthesis

Used ZrO2 modified γ-Al2O3 as support, Co-Ru catalysts were prepared by incipient impregnation method. The effects of impregnation solvents on the performances of catalysts were examined. The catalyst was prepared with ethanol solution and high Co dispersion was obtained, exhibiting highest activity of CO hydrogenation, very low methane selectivity, and high heavy hydrocarbon C5 + selectivity. The catalysts were prepared with aqueous solution and methanol solution, and the reaction behaviors were similar. The solvent isopropanol caused the lowest catalytic activity and highest methane selectivity. Increasing the reaction temperature enhanced the CO hydrogenation rate, and the CO conversion slightly increased the CO2 selectivity and favored the formation methane and light hydrocarbons, while the chain growth probability decreased. For the catalyst prepared with ethanol, the CO conversion, the CH4 selectivity, and the C5 + selectivity were 94.16%, 5.65%, and 88.2%, respectively, and the chain growth probability was 0.87 at 493 K, 1.5 MPa, 800 h−1, and n(H2):n(CO) = 2.0 in feed.

Pretreatment of Alumina and Its Influence on the Properties of Co/Alumina Catalysts for Fischer-Tropsch Synthesis

16.6%Co/γ-Al 2O 3 catalysts prepared by incipient wetness impregnation method were used for Fischer-Tropsch synthesis. The support was pre-treated with different concentration of NH 4NO 3 aqueous solution. The effect of support pre-treatment on the properties of support and performance of supported-cobalt-based catalysts was investigated. To treat the support with NH 4NO 3 aqueous solution enlarged the pore of γAl 2O 3, decreased the impurity Na 2O content, and weakened the surface acidity of γAl 2O 3. The change in the properties of the support decreased the interaction between cobalt species and support, enhanced the CO hydrogenation rate and the C 5+ selectivity. For all catalysts, increasing the reaction temperature increased the CO hydrogenation rate or the CO conversion, slightly decreased the total hydrocarbon selectivity, and favored the formation of methane and light hydrocarbons, while the chain growth probability decreased. For 16.6%Co/γAl 2O 3 catalysts, prepared with the support treated with 100 g/L NH 4NO 3 aqueous solution, the CO conversion, the CH 4 selectivity, and the C 5+ selectivity were 83.13%, 6.86% and 82.75% respectively, and the chain growth probability was 0.83 under the condition of 493 K, 1.5 MPa, 500 h −1 and the molar ratio of H 2 to CO being 2.0 in feed.

Ultrahigh vacuum and high-pressure coadsorption of CO and H2 on Pd(111): A combined SFG, TDS, and LEED study

Sum frequency generation (SFG) vibrational spectroscopy was carried out in conjunction with thermal desorption spectroscopy, low-energy electron diffraction, and Auger electron spectroscopy to examine the coadsorption of CO and H2 on Pd(111). Sequential dosing as well as various CO/H2 mixtures was utilized to study intermolecular interactions between CO and H2. Preadsorbed CO effectively prevented the dissociative adsorption of hydrogen for CO coverages ⩾0.33 ML. While preadsorbed hydrogen was able to hinder CO adsorption at low temperature (100 K), hydrogen was replaced from the surface by CO at 150 K. When 1:1 mixtures of CO/H2 were used at 100 K, hydrogen selectively hindered CO adsorption on on-top sites, while above ∼125 K no blocking of CO adsorption was observed. The observations are explained in terms of mutual site blocking, of a CO–H phase separation, and of a CO-assisted hydrogen dissolution in the Pd bulk. The temperature-dependent site blocking effect of hydrogen is attributed to the ability (inability) of surface hydrogen to diffuse into the Pd bulk above (below) ∼125 K. Nonlinear optical SFG spectroscopy allowed us to study these effects not only in ultrahigh vacuum but also in a high-pressure environment. Using an SFG-compatible ultrahigh vacuum-high-pressure cell, spectra of 1:10 CO/H2 mixtures were acquired up to 55 mbar and 550 K, with simultaneous gas chromatographic and mass spectrometric gas phase analysis. Under reaction conditions, CO coverages ⩾0.5 ML were observed which strongly limit H2 adsorption and thus may be partly responsible for the low CO hydrogenation rate. The high-pressure and high-temperature SFG spectra also showed indications of a reversible surface roughening or a highly dynamic (not perfectly ordered) CO adsorbate phase. Implications of the observed adsorbate structures on catalytic CO hydrogenation on supported Pd nanoparticles are discussed.

CO Hydrogenation on Nickel-Based Catalysts: Effects of Copper Addition

The effect of copper addition on the catalytic properties of silica-supported nickel catalysts for the reaction of CO hydrogenation in the temperature range of 200–500°C has been investigated. Different effects, positive or negative, depending on the temperature and the copper content, are described and explained. At low temperature (230°C), the addition of a low copper content prevents the loss of the active surface by sintering without inhibiting the rate of CO hydrogenation too much. At high temperatures (450°C), high copper content is necessary to limit the accumulation of poisonous carbon products, but at the expense of CO conversion. On the basis of the various kinetic and morphologic effects of copper addition, an advanced description of the CO hydrogenation mechanism is also provided, assuming an active site formed by 2–3 adjacent Ni atoms, whatever the temperature or the copper content may be.

Methanol Synthesis from CO/CO2/H2over Cu/ZnO/Al2O3at Differential and Finite Conversions

Methanol production from CO/CO2/H2over a Cu/ZnO/Al2O3catalyst has been compared in an internal recycle reactor (finite conversion) and a differentially operated tubular reactor. From experiments at differential conversion it was found that the intrinsic rate of CO2hydrogenation was approximately 20 times faster than the intrinsic rate of CO hydrogenation. The rate of methanol production at differential conversion increased almost linearly with respect to the CO2concentration, indicating that there is negligible inhibition by CO2in the absence of products. With 1–4% CO2in the synthesis gas, the methanol production rate was found to be substantially greater at finite conversion than at differential conversion, which is evidence for a promoting influence by the product water. With >4% CO2in the synthesis gas there was increasing loss of methanol production at finite conversion, and under CO2/H2in particular there was an order of magnitude difference between methanol production at finite and differential conversions. This effect was due to inhibition of CO2hydrogenation associated with the presence of product water.

Fischer-Tropsch synthesis on supported cobalt catalysts promoted by platinum and rhenium

An investigation of the CO hydrogenation of Pt- or Re-promoted 8.7 wt% Co/Al2O3 (1.0 wt% Pt or 1.0 wt% Re) has been carried out at two different conditions: 473 K, 5 bar, H2/CO = 2 and 493 K, 1 bar, H2/CO = 7.3. The addition of Pt or Re significantly increases the CO hydrogenation rate (based on weight of Co), but the selectivity was not changed by the presence of Pt or Re. The results show that the observed increases in the reaction rates are caused by increased reducibility and increased number of surface exposed Co-atoms. Steadystate isotopic transient kinetic analysis (SSITKA) with carbon tracing was used to decouple the effects of the concentration of active surface intermediates and the average site reactivity of intermediates during steady-state CO hydrogenation. The SSITKA results show that the concentration of active surface intermediates leading to CH4 increased as a result of the addition of a noble metal promoter. However, the average site activity was not significantly affected upon Re or Pt addition.

Two promoting effects of gadolinium on Ni/SiO 2 catalysis for CO hydrogenation

Promoting effects of Gd and COH interaction in CO hydrogenation on Ni/Gd/SiO 2 catalysts have been investigated by means of kinetics, TPR, and FT-IR. The reaction rate of CO hydrogenation on Ni/Gd/SiO 2 was about five times faster than that on Ni/SiO 2 above 500 K. The IR band of side-on CO (NiCOGd) on Ni/Gd/SiO 2 was observed at 1600 cm −1 in addition to the bands of on-top (ca. 2040 cm −1) and bridge CO (ca. 1950 cm −1). All side-on CO easily dissociates, whereas most on-top Gd exists as partially reduced GdO x and the GdO x acts as a reservoir of hydrogen. A new peak due to GdH was observed at 1610 cm −1 under reaction conditions. The adsorbed hydrogen increased the amount of CO adsorbed on Ni/Gd/SiO 2. Consequently, the easy dissociation of CO and the storage of hydrogen on the Ni/Gd/SiO 2 catalyst promoted the hydrogenation of CO to hydrocarbons (mainly methane).

Importance of surface hydrogen concentration in enhancing activity of CoNi alloy catalyst for CO hydrogenation

The hydrogen—deuterium exchange reaction was employed for studying the reactivity of adsorbed hydrogen on CoNi alloy. The infrared spectra of adsorbed NO indicates that the support oxide electronically interacts with the CONi alloy. Desorption measurements suggest that the electron density of the alloy greatly influences the surface coverage of hydrogen and carbon monoxide. The CO hydrogenation rate of CoNi alloy in the presence of CO was shown to be related to the H 2D 2 exchange rate. The dissociative adsorption of hydrogen in the presence of CO is of primary importance in determining the CO hydrogenation rate of the CoNi alloy system, since the preadsorbed CO species strongly hinder the hydrogen adsorption. A high surface concentration of active hydrogen in the presence of CO leads to high catalytic activity for CO hydrogenation on CoNi alloy.

The effect of supports on the activity and selectivity of CoNi alloy catalysts for CO hydrogenation

The CO hydrogenation activity of 50Co50Ni alloy catalysts strongly depended on the oxide support. Electron-donating oxides such as MgO, PbO, and ZnO lowered the overall activity of the 50Co50Ni metal. The CO conversion as well as the chain growth probability was high over 50Co50Ni/TiO 2 and 50Co50Ni/MnO 2. The infrared spectra of adsorbed NO indicated that the electron density of the 50Co50Ni metal was low when it was supported on electron-accepting oxide. The results of desorption measurements suggest that metal-support interaction has a great influence on the surface concentration of hydrogen and carbon monoxide, and adsorption of carbon monoxide and hydrogen is weakened by increasing the electronegativity of the oxide support. Since the rate of H 2D 2 exchange correlated well with the CO hydrogenation rate, activation of hydrogen is of primary importance in this catalyst system. The low electron density of the alloy supported on the electron-accepting oxides such as TiO 2 and SiO 2 weakens CO adsorption, resulting in an increase in surface coverage of hydrogen. Thus sufficient coverage of hydrogen leads to a high CO hydrogenation rate.

Site transfer and a support-bound HCO Complex on Ni/TiO 2

Temperature-programmed reaction and desorption and isotope labeling are used to identify two forms of adsorbed CO, one on Ni metal and the other adsorbed as a HCO complex on the support of a Ni/TiO 2 catalyst. The complex, which appears to be a methoxy species, forms by an activated process in which CH 3O or H and CO spill over onto the TiO 2 surface. The rate of spillover is much slower than the rate of CO hydrogenation on Ni/TiO 2 at 385 K. The rate of spillover is also much slower than that observed for the same process on Ni/Al 2O 3 catalysts. Because CO on Ni hydrogenates to CH4 faster than the HCO complex, CH4 forms in two distinct peaks on Ni/TiO 2 during TPR of adsorbed CO, and isotope labeling shows that CO adsorbed on these two sites do not interact significantly. Evidence is also presented to show that reverse transfer of the complex from the TiO 2 to the Ni surface readily occurs between 425–455 K in the absence of gas-phase H 2.

Multiple reaction states in CO hydrogenation on alumina-supported cobalt catalysts

CO hydrogenation was studied on four (1, 3, 10 and 15 wt%) Co Al 2O 3 catalysts using the technique of temperature-programmed surface reaction (TPSR). Two distinct methane peaks (Peaks A and B) are observed for 3, 10 and 15% Co Al 2O 3 during TPSR of chemisorbed CO at room temperature, indicating the presence of two different reaction states or mechanisms for CO hydrogenation ( A and B). No methane peak is observed for 1% Co Al 2O 3 unless it is reduced at 1023 K. The more active A state, the relative population of which increases with increasing metal loading and increasing extent of reduction, probably corresponds to hydrogenation of atomic carbon on 3 D cobalt crystallites while the less active B state is assigned to decomposition on metal crystallites of a methoxy or formate species originally formed on the support from spilled-over hydrogen and carbon monoxide. TPSR spectra of hydrogen with carbon deposited by CO dissociation at 523 K show that the quantity of active α-carbon increases with increasing metal loading and correlates with the relative population of A sites. A linear correlation between logarithm of the steady-state methane turnover frequency and the relative population of A sites suggests that large variations in the steady-state CO hydrogenation rate with dispersion and metal loading observed for these catalysts may be explained in terms of variations in the distribution of reaction states for CO hydrogenation, i.e., a larger fraction of Reaction A at higher metal loadings and higher extents of reduction.

Potassium promotion of Ni/Al 2O 3 catalysts

Potassium promotion of Ni/Al 2O 3 catalysts was studied using steady-state CO hydrogenation, temperature-programmed reaction (TPR) of adsorbed CO with flowing H 2, and temperature-programmed desorption (TPD) of CO and H 2. Two series of catalysts were used; the potassium concentration was varied in one series and the nickel concentration in the other series. Potassium promotion decreased the specific activity for methane formation from both CO adsorbed on nickel and the H CO complex adsorbed on the Al 2O 3, and it increased the CO dissociation rate on nickel. In addition, potassium inhibited the transfer of CO from nickel to Al 2O 3 and poisoned the adsorption sites on Al 2O 3. Much of the potassium was on the Al 2O 3 surface and thus the number of adsorption sites on nickel did not change significantly. Potassium decreased the steady-state rate of CO hydrogenation on Ni/Al 2O 3 catalysts, but the decrease was much smaller than seen on Ni/SiO 2 catalysts because much of the potassium was on the Al 2O 3. Potassium increased selectivity to olefins and higher hydrocarbons. Because potassium was on both the support and the nickel, the K:(Ni+Al 2O 3) ratio appears to be a better measure of the catalytic activity than the K:Ni ratio. Good agreement was obtained between steady-state kinetics and TPR.

Comparison of catalytic properties of Ni/CeO2 and Ni/La2O3 prepared by low-temperature oxidation.

An attempt was made with rare earth intermetallic compounds to prepare highly active catalysts by low-temperature oxidation. CeNi5 was chosen as the starting material, because works on LaM5 have shown that surface area increase and Ni crystallite growth are closely related to oxidation rate, and because the Ce oxidation rate is much higher than that of La. It was found that low-temperature oxidation of CeNi5 was accompanied by an increase in surface area without the growth of Ni crystallites. The reaction rate of CO hydrogenation per Ni weight was about 500-fold higher for Ni/CeO2 than for Ni/La2O3 at 535 K. This was connected with increased Ni surface area (180-fold) and high turnover frequency (2.8-fold). Moreover, C2 and C3 products increased with increasing conversion of Ce oxidation.