CO Dissociation Energy Research Articles

Analyzing characteristic and modeling of high-temperature proton exchange membrane fuel cells with CO poisoning effect

High-temperature proton exchange membrane fuel cells (HT-PEMFC) have strong resistance to CO poisoning. However, the published CO poisoning models for HT-PEMFC are based on the finite element analysis method, which are difficult to use for the performance prediction and development of system control strategies due to a large amount of calculation. In the beginning, a semi-empirical model of HT-PEMFC is deduced based on the analysis of the CO poisoning characteristics. Then the key parameters of ohmic impedance and concentration polarization advance correction factor are obtained by fitting the polarization curves, dissociation and adsorption activation energy of H2 and CO are obtained by the calculation, respectively. The slope of the straight line segment in the ohmic polarization interval of the polarization curve is linearly related to ln[H2/CO]. The change of limiting current density is the main factor for the advance of concentration polarization. The fitted ohmic impedance varies with temperature and CO concentration, but changes little above 175 °C. CO coverage depends primarily on dissociation and adsorption activation energy of CO. Subsequently, the proposed model is validated with experimental data and shows high similarity. The model can be used for studying the systematic control strategy development and performance monitoring of HT-PEMFC.

Effects of composition on catalytic activities of molybdenum doped platinum nanoparticles.

The physical and chemical properties of bimetallic nanoparticles can be optimized by tuning the particle composition. In this study, we identified CO adsorption and dissociation energetics on five Pt-Mo nanoparticles at different concentrations, the lowest energy Pt7, Pt6Mo, Pt5Mo2, Pt4Mo3, and Mo7 clusters. We have shown that the CO adsorption and dissociation energies and preferred CO adsorption sites are largely dependent on the composition of the nanoparticles. As the Mo concentration increases, the strength of the C-O internal bond in the adsorption complex decreases, as indicated by a decrease in the C-O stretching frequency. Also, more Mo sites in the nanoparticle become available for CO adsorption, and the preferred CO adsorption site switches from Pt to Mo. For these reasons, dissociation of CO is energetically favorable on Pt4Mo3 and Mo7. On both compositions, we have shown that the dissociation paths begin with CO adsorbed on a Mo site in a multifold configuration, in particular in a tilted configuration. These findings provide insight on the effects of the composition on the chemical and catalytical properties of Pt-Mo nanoparticles, thereby guiding future experiments on the synthesis of nanoparticles, especially those that may be suitable for various desired applications containing CO.

Adsorption and dissociation of carbon monoxide on rhodium surface: AB INITIO study

Ab initio molecular dynamics simulations of carbon monoxide adsorption and dissociation on Rh(100), Rh(110), and Rh(111) surfaces have been performed using projector augmented wave (PAW) pseudopotential and Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional. The results reveal the C-downward configuration is the most preferable configuration for CO molecules on rhodium surface. CO dissociation energies at Rh(100) hollow site, Rh(110) bridge site, and Rh(111) hollow site are 1.64 eV, 0.05 eV, and 0.91 eV, respectively, which are much lower than that in vacuum (13.19 eV). The minimum energy barrier calculated by nudged elastic band (NEB) method indicates Rh(110) surface provides the highest activity by lowering the energy barrier and dissociation energy by ∼13eV.

Tuning Ion-Pair Interaction in Cuprous-Based Protic Ionic Liquids for Significantly Improved CO Capture

Because of the high bond dissociation energy of CO, achieving efficient absorption of CO in liquid solvents is still a significant challenge in gas separation. Herein, it is unprecedently found tha...

Binuclear pentalene titanium carbonyls involved in the deoxygenation of carbon dioxide

The complete series of binuclear pentalene titanium carbonyls Pn2Ti2(CO)n and Pn†2Ti2(CO)n (Pn = pentalene; Pn† = 1,4-(iPr3Si)2C8H4; n = 0, 1, 2, 3, 4), including Pn†2Ti2(CO)2 obtained experimentally from Pn†2Ti2 and carbon dioxide, have been investigated by density functional theory. For the carbonyl-free Pn2Ti2 system the singlet structure is found to lie 22.5 and 18.5 kcal/mol in energy below the isomeric triplet and quintet structures, respectively. However, for the experimentally known Pn†2Ti2 system (Pn† = 1,3-(iPr3Si)2C8H4) the singlet, triplet, and quintet spin state structures have essentially equal energies within 0.3 kcal/mol suggesting the possibility of complicated magnetic behavior. The Ti–Ti distance of 2.399 Å found in crystalline Pn†2Ti2 by X-ray crystallography is closest to the 2.415 Å Ti-Ti distance predicted for the triplet spin state structure. Carbonylation of Pn2Ti2 results in successive lengthening of the Ti-Ti distance as CO groups are added. Three CO groups are the maximum number that can be introduced into a viable Pn2Ti2(CO)n derivative as indicated by the predicted exothermic CO dissociation energy of the tetracarbonyl Pn2Ti2(CO)4. The lowest energy structure for the monocarbonyl Pn2†Ti2(CO) has a four-electron donor bridging η2-μ-CO group in accord with the experimental structure. The lowest energy structure for the dicarbonyl Pn†2Ti2(CO)2 has exclusively terminal CO groups in a cis configuration, again in accord with the experimental Pn†2Ti2(CO)2 structure. Two terminal CO groups are accompanied by a third highly unsymmetrical semibridging CO group in the lowest energy structures for the tricarbonyls Pn2Ti2(CO)3 and Pn†2Ti2(CO)3. However, the lowest energy structures for the tetracarbonyls Pn2Ti2(CO)4 and Pn†2Ti2(CO)4 have exclusively terminal CO groups.

Mechanical Stress Combined with Alloying May Allow Continuous Control Over Reactivity: Strain Effects on CO Dissociation and Subsequent Methanation Catalysis over Ni(211), Ni3Fe(211), and NiFe(112)

Mechanical stress combined with alloying as controlled by CO dissociation is investigated for the control of methanation activity. CO dissociation over strained Ni(211), Ni3Fe(211), and NiFe(112) is investigated. A continuous 0.62 eV range of CO reaction energy is achievable considering the examined alloys and strains. The CO dissociation energy spanned by the strained NixFey surfaces includes that of elemental Ni, Ru, Co, Rh, and Ir. The linear relationship between activation energy and reaction energy is found to be the same under strain as under alloying, suggesting strain as a similar alchemical tool. Peak activity is achievable for each alloy depending on the selection of strain.

In Search of Initial Predictors of Fischer–Tropsch Catalytic Activity

All Fischer–Tropsch mechanisms known to date begin with the adsorption of carbon monoxide followed by its dissociation on a given catalysts surface. Understanding how those catalysts modify reactivity descriptors such as CO adsorption and dissociation energies is a key for nanoengineering materials for this type of applications. Cluster models of Co, Fe, Ni, Pd, Pt, and Ru have been explored using the density functional theory, in search of initial descriptors of Fischer–Tropsch activity for pure and binary combinations of those elements. Carbon monoxide adsorption energies were calculated for adsorption on all possible catalytic sites, and the most preferred CO adsorption sites were found in each case. An initial predictor that can be used to anticipate potentially effective catalysts was identified as a percentage difference, using CO adsorption energy results in combination with CO dissociation energies from the previously found sites. A greater catalysts performance is expected when that percentage difference is maximized. On pure clusters, the predictor indicates that ruthenium is expected to be the best catalyst followed by cobalt, in very good agreement with the current knowledge in this field. Thus, this paper presents a mechanism to quickly explore the natural potential of a catalyst material to break the CO bond. The predictor presented here can guide the synthesis of new catalysts, involving modifications of known and currently used catalysts for the Fischer–Tropsch process, and investigations on catalysis in general.

Importance of Long-Range Noncovalent Interactions in the Regioselectivity of Rhodium-Xantphos-Catalyzed Hydroformylation

M06-L-based quantum chemical calculations were performed to examine two key elementary steps in rhodium (Rh)-xantphos-catalyzed hydroformylation: carbonyl ligand (CO) dissociation and the olefin insertion into the Rh–H bond. For the resting state of the Rh-xantphos catalyst, HRh(xantphos)(CO)2, our M06-L calculations were able to qualitatively reproduce the correct ordering of the equatorial–equatorial (ee) and equatorial–axial (ea) conformers of the phosphorus ligands for 16 derivatives of the xantphos ligand, implying that the method is sufficiently accurate for capturing the subtle energy differences associated with various conformers involved in Rh-catalyzed hydroformylation. The calculated CO dissociation energy from the ea conformer (ΔE = 21–25 kcal/mol) was 10–12 kcal/mol lower than that from the ee conformer (ΔE = 31–34 kcal/mol), which is consistent with prior experimental and theoretical studies. The calculated regioselectivities for propene insertion into the Rh–H bond of the ee-HRh(xantphos)(propene)(CO) complexes were in good agreement with the experimental l:b ratios. The comparative analysis of the regioselectivities for the pathways originating from the ee-HRh(xantphos)(propene)(CO) complexes with and without diphenyl substituents yielded useful mechanistic insight into the interactions that play a key role in regioselectivity. Complementary computations featuring xantphos ligands lacking diphenyl substituents implied that the long-range noncovalent ligand–ligand and ligand–substrate interactions, but not the bite angles per se, control the regioselectivity of Rh-diphosphine-catalyzed hydroformylation of simple terminal olefins for the ee isomer. Additional calculations with longer chain olefins and the simplified structural models, in which the phenyl rings of the xantphos ligands were selectively removed to eliminate either substrate–ligand or ligand–ligand noncovalent interactions, suggested that ligand–substrate π-HC interactions play a more dominant role in the regioselectivity of Rh-catalyzed hydroformylation than ligand–ligand π–π interactions. The present calculations may provide foundational knowledge for the rational design of ligands aimed at optimizing hydroformylation regioselectivity.

The catalytic methanation of coke oven gas over Ni-Ce/Al2O3 catalysts prepared by microwave heating: Effect of amorphous NiO formation

Ni-Ce/γ-Al2O3 catalysts were prepared by traditional and microwave heating and tested by the methanation of simulated coke oven gas in a fixed bed reactor. Various characterization techniques were used to examine the bulk and surface properties of the catalysts. The catalysts obtained by microwave heating show superior methanation activity to traditional catalysts. Conversion of 100% CO, CO2, and O2, with part conversion of C2H6, was obtained on the MO-15NC catalyst with the following reaction conditions: 260°C, 3.0MPa and 20,000mLg−1h−1 weight hourly space velocity. The temperature gradient between the NiO and the alumina support caused by the difference in microwave energy absorption promotes the formation of a large amount of highly dispersed amorphous NiO with a Ni loading of less than 15wt%, and is more active for the methanation reaction because of a weak interaction with the support, large active surface area and low CO dissociation energy.

Copper Promotion in CO Adsorption and Dissociation on the Fe(100) Surface

Spin-polarized density functional theory computations have been carried out to study the adsorption and dissociation of CO on clean as well as nCu-adsorbed and nCu-substituted Fe(100) surfaces (n = 1–3) at different coverage to explore the Cu promotion effect in CO activation. Increasing Cu content not only lowers CO dissociation energies but also increases CO dissociation barriers as well as making CO dissociation thermodynamically less favorable, and the clean Fe(100) surface is most active in CO adsorption and dissociation. The nCu-substituted Fe(100) surface can suppress CO adsorption and dissociation more strongly than the nCu-adsorbed Fe(100) surface. CO stretching frequencies at different coverages have been computed for assisting experimental investigations.

Diverse bonding modes of the pentalene ligand in binuclear cobalt carbonyl complexes

The 2007 synthesis of the hexamethylpentalene complex cis-(η5,η5-C8Me6)Co2(CO)4 by O’Hare and coworkers makes of interest a theoretical study of the unsubstituted binuclear pentalene cobalt carbonyls (C8H6)Co2(CO)n (n=6, 5, 4, 3). In this connection an unbridged unsubstituted cis-(η5,η5-C8H6)Co2(CO)4 structure analogous to the experimental hexamethyl structure is found to be the lowest energy (C8H6)Co2(CO)4 structure. Furthermore, this (C8H6)Co2(CO)n structure is predicted to be the product from reactions of pentalene derivatives with cobalt carbonyls based on the thermochemistry of CO dissociation energies in the sequence n=6 → 5 → 4 → 3 → 2. The low-energy structures for the unsaturated (C8H6)Co2(CO)n (n=3, 2) derivatives also have the pentalene ligand bonded to each cobalt as a pentahapto ligand. They may be derived from either this unbridged cis-(η5,η5-C8H6)Co2(CO)4 structure or a doubly CO-bridged variation thereof by removal of one or two CO groups. The carbonyl-rich (C8H6)Co2(CO)n (n=6, 5) structures, which may be considered as precursors to cis-(η5,η5-C8H6)Co2(CO)4, illustrate considerable diversity of bonding modes of the pentalene ligand to the central Co2 unit. Structures without direct Co–Co bonds are found exhibiting either cis or trans stereochemistry in which trihapto allylic and/or pentahapto cyclopentadienylic subunits are bonded to Co(CO)3 and Co(CO)2 moieties, respectively. In addition, (C8H6)Co2(CO)n (n=6, 5) structures exhibiting cis stereochemistry are found in which CC bonds of a butadiene or fulvene subunit of the pentalene ligand replace CO groups in Co2(CO)8, retaining the formal Co–Co single bond.

First principle and ReaxFF molecular dynamics investigations of formaldehyde dissociation on Fe(100) surface

Detailed formaldehyde adsorption and dissociation reactions on Fe(100) surface were studied using first principle calculations and molecular dynamics (MD) simulations, and results were compared with available experimental data. The study includes formaldehyde, formyl radical (HCO), and CO adsorption and dissociation energy calculations on the surface, adsorbate vibrational frequency calculations, density of states analysis of clean and adsorbed surfaces, complete potential energy diagram construction from formaldehyde to atomic carbon (C), hydrogen (H), and oxygen (O), simulation of formaldehyde adsorption and dissociation reaction on the surface using reactive force field, ReaxFF MD, and reaction rate calculations of adsorbates using transition state theory (TST). Formaldehyde and HCO were adsorbed most strongly at the hollow (fourfold) site. Adsorption energies ranged from -22.9 to -33.9 kcal/mol for formaldehyde, and from -44.3 to -66.3 kcal/mol for HCO, depending on adsorption sites and molecular direction. The dissociation energies were investigated for the dissociation paths: formaldehyde → HCO + H, HCO → H + CO, and CO → C + O, and the calculated energies were 11.0, 4.1, and 26.3 kcal/mol, respectively. ReaxFF MD simulation results were compared with experimental surface analysis using high resolution electron energy loss spectrometry (HREELS) and TST based reaction rates. ReaxFF simulation showed less reactivity than HREELS observation at 310 and 523 K. ReaxFF simulation showed more reactivity than the TST based rate for formaldehyde dissociation and less reactivity than TST based rate for HCO dissociation at 523 K. TST-based rates are consistent with HREELS observation.

Extreme Metal Carbonyl Back Bonding in Cyclopentadienylthorium Carbonyls Generates Bridging C2O2 Ligands by Carbonyl Coupling

Laboratory studies of the interaction of carbon monoxide with organoactinides result in the formation of isolable complexes such as Cp3UCO derivatives (Cp = cyclopentadienyl) as well as coupling reactions to give derivatives of the oligomeric anions C(n)O(n)(2-) (n = 2, 3, 4). To gain some insight into actinide carbonyl chemistry, binuclear cyclopentadienylthorium carbonyls Cp2Th2(CO)n (n = 2 to 5) as model compounds have been investigated using density functional theory. The most favorable such structures in terms of energy and thermochemistry are the tricarbonyl Cp2Th2(η(2)-μ-CO)3 having three four-electron donor bridging carbonyl groups and the tetracarbonyl Cp2Th2(η(4)-μ-C2O2)(η(2)-μ-CO)2 having not only two four-electron donor bridging carbonyl groups but also a bridging ethynediolate ligand formed by coupling two CO groups through C-C bond formation. The bridging infrared ν(CO) frequencies ranging from 1140 to 1560 cm(-1) in these Cp2Th2(CO)n (n = 3, 4) derivatives indicate extremely strong Th→CO back bonding in these structures, corresponding to formally dianionic CO(2-) and C2O2(2-) ligands and the favorable +4 thorium oxidation state. A characteristic of the Cp2Th2(η(2)-μ-CO)3 and Cp2Th2(η(4)-μ-C2O2)(η(2)-μ-CO)2 structures is their ability to add terminal CO groups, preferably to the thorium atom bonded to the fewest oxygen atoms. These terminal CO groups exhibit ν(CO) frequencies in a similar range as terminal CO groups in d-block metal carbonyls. However, these terminal CO groups are relatively weakly bonded to the thorium atoms as indicated by predicted CO dissociation energies of 14 kcal/mol for Cp2Th2(CO)5. Two low energy structures for the dicarbonyl Cp2Th2(CO)2 are found with two separate four-electron donor bridging CO groups and relatively short Th-Th distances of 3.3 to 3.4 Å suggesting formal single bonds and +3 thorium formal oxidation states. However, a QTAIM analysis of this formal Th-Th bond does not reveal a bond critical point thus suggesting a multicenter bonding model involving the bridging CO groups.

A computational study of the CO dissociation in cyclopentadienyl ruthenium complexes relevant to the racemization of alcohols

The formation of an active 16-electron ruthenium sec-alkoxide complex via loss of the CO ligand is an important step in the mechanism of the racemization of sec-alcohols by (η(5)-Ph(5)C(5))Ru(CO)(2)X ruthenium complexes with X = Cl and O(t)Bu. Here we show with accurate DFT calculations the potential energy profile of the CO dissociation pathway for a series of relevant (η(5)-Ph(5)C(5))Ru(CO)(2)X complexes, where X = Cl, O(t)Bu, H and COO(t)Bu. We have found that the CO dissociation energy increases in the following order: O(t)Bu (lowest), Cl, COO(t)Bu and H (highest). Using the distance between ruthenium and C(CO), r = Ru-C(CO), as a constraint, and by optimizing all other degrees of freedom for a range of Ru-CO distances, we obtained relative energies, ΔE(r) and geometries of a sufficient number of transient structures with the elongated Ru-CO bond up to r = 3.4 Å. Our calculations provide a quantitative understanding of the CO ligand dissociation in (η(5)-Ph(5)C(5))Ru(CO)(2)Cl and (η(5)-Ph(5)C(5))Ru(CO)(2)(O(t)Bu) complexes, which is relevant to the mechanism of their catalytic activity in the racemization of alcohols. We recently reported that exchange of the CO ligand by isotopically labeled (13)CO in the Ru-O(t)Bu complex occurs twenty times faster than that in the Ru-Cl complex. This corresponds to a difference of 1.8 kcal mol(-1) in the CO dissociation energy (at room temperature). This is in very good agreement with the calculated difference between the two potential energy curves for Ru-O(t)Bu and Ru-Cl complexes, which is about 1.8-2 kcal mol(-1) around the corresponding transition states of the CO dissociation. The calculated difference in the total energy for CO dissociation in (η(5)-Ph(5)C(5))Ru(CO)(2)X complexes is related to the stabilization provided by the X group in the final 16-electron complexes, which are formed via product-like transition states. In addition to the calculated transition states of CO dissociation in Ru-O(t)Bu and Ru-Cl complexes, the calculated transient structures with the elongated Ru-CO bond provide insight into how the geometry of the ruthenium complex with a potent heteroatom donor group (X) gradually changes when one of the COs is dissociating.

Diverse bonding modes of the tetramethyleneethane ligand in binuclear iron carbonyl derivatives

The tetramethyleneethane (TME) iron carbonyl derivative cis-(η3,η3-TME)Fe2(CO)6 has long been known as a product from the reaction of allene with iron carbonyls. Theoretical studies on the (TME)Fe2(CO)6 system show this experimentally observed singlet cis bis(allyl) structure with an Fe–Fe bond length of ∼2.9 A to be the lowest energy structure. However, three other singlet (TME)Fe2(CO)6 structures lying in energy within 10 kcal mol−1 of this global minimum exhibit different modes of bonding of the TME ligand to the Fe2(CO)6 unit including cis and trans bis(butadiene) structures and a trans bis(trimethylenemethane) structure. The lowest energy structure for the heptacarbonyl (TME)Fe2(CO)7 has four TME carbon atoms bonded to an Fe(CO)3 unit as a butadiene ligand with the remaining two TME carbon atoms forming a five-membered FeC4 chelate ring. The lowest energy (TME)Fe2(CO)8 structure has one Fe(CO)4 unit bonded to a TME CC double bond and the other Fe(CO)4 unit bonded to two external TME carbon atoms to form a five-membered FeC4 chelate ring thereby leaving an uncomplexed CC double bond. The octacarbonyl (TME)Fe2(CO)8 is disfavored relative to CO loss to give the heptacarbonyl (TME)Fe2(CO)7. The heptacarbonyl is marginally viable with a low but endothermic CO dissociation energy of ∼11 kcal mol−1 to give the hexacarbonyl (TME)Fe2(CO)6. This thermochemistry can account for the experimental observation of the hexacarbonyl (TME)Fe2(CO)6 rather than carbonyl richer species as products from the reactions of allene with iron carbonyls.

Ligand Effects on Reactivity of Cobalt Acyl Complexes

Hydrogenolysis reactions of cobalt acyl complexes, [Co(CO)3(L)(COR)] (L = phosphine, R = Me, nPr) have been monitored using in situ IR spectroscopy at moderate temperatures (<75 °C) and pressures (<25 bar). The reactions provide a model for the product-formation step in phosphine-modified, cobalt-catalyzed hydroformylation. The reaction kinetics are dependent on L, with the fastest rate being observed for the complex containing n-pentyl-9-phosphabicyclo[4.2.1]nonane (a5-PhobPC5). The observed dependence of rate on H2 and CO pressure is consistent with a mechanism involving initial CO dissociation, followed by reaction of [Co(CO)2(L)(COR)] with H2. Isotopic exchange experiments, monitored by IR spectroscopy, demonstrate that both terminal and acetyl carbonyls of [Co(CO)3(L)(COR)] exchange with free 13CO. Kinetic data are also reported for reactions of [Co(CO)3(L)(COR)] with triphenyltinhydride. A zero-order dependence on [Ph3SnH] (at large excess) and positive values of ΔS‡ demonstrate rate-determining CO dissociation. For a series of less bulky, symmetrical phosphines, the rates follow the sequence PEt3 < PMe2Ph ∼ PEtPh2 < PPh3 < P(4-ClC6H4)3, in accord with their electron-donating strength. Higher rates are found for more bulky phosphines, and the fastest rate is again found for L = a5-PhobPC5. Calculations using density functional theory indicate that the CO dissociation energy for [Co(CO)3(L)(COMe)] is influenced by the stereoelectronic properties of L, with steric bulk having a substantial effect. X-ray crystal structures are reported for [Co(CO)3(PEtPh2)(COMe)], [Co(CO)3(s-PhobPC5)]2, and [Co(CO)3(a5-PhobPC5)]2.

Hydrogenation of CO to Methane Over Mesoporous Nickel–Iron–Alumina Xerogel Nano-Catalysts

Mesoporous nickel-iron-alumina xerogel ((40-x)Ni(x)FeAX) nano-catalysts with different iron content (x = 0, 2.5, 5, 7.5, and 10) were prepared by a single-step sol-gel method for use in the methane production from carbon monoxide and hydrogen. The effect of iron content on the catalytic performance of (40-x)Ni(x)FeAX catalysts was investigated. In the methanation reaction, yield for CH4 decreased in the order of 35Ni5FeAX > 32.5Ni7.5FeAX > 30Ni10FeAX > 37.5Ni2.5FeAX > 40Ni0FeAX. This indicated that optimal iron content of mesoporous nickel-iron-alumina xerogel nano-catalyst was required for maximum production of CH4 in the methanation reaction. Experimental results revealed that optimal CO dissociation energy and large H2 adsorption ability of the catalyst were favorable for methane production. Among the catalysts tested, 35Ni5FeAX catalyst, which retained the most optimal CO dissociation energy and the largest H2 adsorption ability, exhibited the best catalytic performance in terms of conversion of CO and yield for CH4 in the methanation reaction. CO dissociation energy and H2 adsorption ability of the catalyst played a key role in determining the catalytic performance of (40-x)Ni(x)FeAX in the methanation reaction.

Methanation of Carbon Dioxide Over Mesoporous Nickel–M–Alumina (M = Fe, Zr, Ni, Y, and Mg) Xerogel Catalysts: Effect of Second Metal

Mesoporous nickel (35 wt%)–M (5 wt%)–alumina xerogel (denoted as 35Ni5MAX) catalysts with different second metal (M = Fe, Zr, Ni, Y, and Mg) were prepared by a single-step sol–gel method for use in the methane production from carbon dioxide and hydrogen. In the carbon dioxide methanation reaction, yield for CH4 decreased in the order of 35Ni5FeAX > 35Ni5ZrAX > 35Ni5NiAX > 35Ni5YAX > 35Ni5MgAX. This indicated that the catalytic performance was greatly influenced by the identity of second metal in the carbon dioxide methanation reaction. Experimental results revealed that CO dissociation energy and metal-support interaction of the catalyst played key roles in determining the catalytic performance of 35Ni5MAX catalysts in the reaction. Among the catalysts tested, 35Ni5FeAX catalyst, which retained the most optimal CO dissociation energy and the weakest metal-support interaction, exhibited the best catalytic performance in terms of conversion of CO2 and yield for CH4. In the carbon dioxide methanation over mesoporous nickel–M–alumina xerogel catalysts with different second metal (M = Fe, Zr, Ni, Y, and Mg), yield for CH4 increased with decreasing TPSR peak temperature and with decreasing metal-support interaction of the catalyst.

Hydrogenation of carbon monoxide to methane over mesoporous nickel-M-alumina (M = Fe, Ni, Co, Ce, and La) xerogel catalysts

Mesoporous nickel(30 wt%)-M(10 wt%)-alumina xerogel (30Ni10MAX) catalysts with different second metal (M = Fe, Ni, Co, Ce, and La) were prepared by a single-step sol–gel method for use in the methane production from carbon monoxide and hydrogen. In the methanation reaction, yield for CH 4 decreased in the order of 30Ni10FeAX > 30Ni10NiAX > 30Ni10CoAX > 30Ni10CeAX > 30Ni10LaAX. Experimental results revealed that CO dissociation energy of the catalyst and H 2 adsorption ability of the catalyst played a key role in determining the catalytic performance of 30Ni10MAX catalyst in the methanation reaction. Optimal CO dissociation energy of the catalyst and large H 2 adsorption ability of the catalyst were favorable for methane production. Among the catalysts tested, 30Ni10FeAX catalyst with the most optimal CO dissociation energy and the largest H 2 adsorption ability exhibited the best catalytic performance in terms of conversion of CO and yield for CH 4 in the methanation reaction. The enhanced catalytic performance of 30Ni10FeAX was also due to a formation of nickel–iron alloy and a facile reduction.

Binuclear Pentalene Iron Carbonyl Complexes

AbstractThe bicyclic hydrocarbon pentalene, although unstable in the free state, forms a stable iron carbonyl derivative cis‐(η5,η5‐C8H6)Fe2(CO)4(μ‐CO). In this connection, the series of binuclear pentalene iron carbonyl derivatives C8H6Fe2(CO)n (n = 7, 6, 5, 4) have been investigated by density functional theory. The lowest energy C8H6Fe2(CO)6 structure is predicted to be trans‐(η5,η5‐C8H6)Fe2(CO)6 without an iron–iron bond. However, a cis‐(η5,η1‐C8H6)Fe2(CO)6 structure with an uncomplexed pentalene C=C double bond and a formal Fe–Fe bond of length 2.646 Å (BP86) lies only ca. 3 kcal/mol above this global minimum. The CO dissociation energy of C8H6Fe2(CO)6 to give C8H6Fe2(CO)5 is predicted to be only ca. 12 kcal/mol, explaining the formation of C8H6Fe2(CO)5 rather than C8H6Fe2(CO)6 in reactions of dihydropentalene with iron carbonyls. In addition, the experimentally known cis‐(η5,η5‐C8H6)Fe2(CO)4(μ‐CO) structure is found to be the lowest energy C8H6Fe2(CO)5 structure by more than 25 kcal/mol (BP86). For the tetracarbonyl two triplet and two singlet cis‐C8H6Fe2(CO)4 structures lie within 7 kcal/mol of each other (BP86) with the triplet structures being of slightly lower energies. The singlet C8H6Fe2(CO)4 structure is predicted to be thermodynamically unfavorable with respect to disproportionation into C8H6Fe2(CO)5 + C8H6Fe2(CO)3.