Acrolein Hydrogenation on Ni(111)

Acrolein hydrogenation via allyl alcohol, propanal, and enol into propanol on the Ni(111) surface has been investigated using the spin-polarized periodic density functional theory method. On the basis of the computed adsorption energies and effective hydrogenation barriers, acrolein hydrogenation into propanal and allyl alcohol obeys the Langmuir–Hinshelwood mechanism and propanal formation is more favored kinetically and thermodynamically than allyl alcohol formation. Hydrogenation of propanal and allyl alcohol should follow the Eley–Rideal mechanism. The adsorption energies of acrolein, allyl alcohol, and propanal along with the partial hydrogenation selectivity on Ni, Au, Ag, and Pt catalysts have been compared and discussed

Mechanisms of CO Activation, Surface Oxygen Removal, Surface Carbon Hydrogenation, and C–C Coupling on the Stepped Fe(710) Surface from Computation

To understand the initial steps of Fe-based Fischer–Tropsch synthesis, systematic periodic density functional theory computations have been performed on the single-atom stepped Fe(710) surface, composed by <i>p</i>(3 × 3) Fe(100)-like terrace and <i>p</i>(3 × 1) Fe(110)-like step. It is found that CO direct dissociation into surface C and O is more favored kinetically and thermodynamically than the H-assisted activation via HCO and COH formation. Accordingly, surface O removal by hydrogen via H₂O formation is the only way. On the basis of surface CH_<i>x</i> hydrogenation (<i>x</i> = 0, 1, 2, 3), surface CH_<i>x</i> + CH_<i>x</i> coupling and CO + CH_<i>x</i> insertion resulting in CH_<i>x</i>CO formation followed by C–O dissociation, surface C hydrogenation toward CH₃ formation is more favored kinetically than the formation of CH_<i>x</i>-CH_<i>x</i> and CH_<i>x</i>CO, as well as thermodynamically. Starting from CH₃, the formation of CH₄ and CH₃CO has similar barriers and endothermic reaction energies, while CH₃CO dissociation into CH₃C + O has low barrier and is highly exothermic. Therefore, turning the H₂/CO ratio should change the selectivity toward C–C formation and propagation

Reactions of CO, H₂O, CO₂, and H₂ on the Clean and Precovered Fe(110) Surfaces – A DFT Investigation

The reactions of CO and H₂O on the clean Fe(110) surface as well as surfaces with 0.25 monolayer O, OH, and H precoverage have been computed on the basis of density functional theory (GGA-PBE). Under the considerations of the reductive nature of CO as reactant and H₂ as product as well as the oxidative nature of CO₂ and H₂O, we have studied the potential activity of metallic iron in the water-gas shift reaction. On the clean surface, CO oxidation following the redox mechanism has a similar barrier as CO dissociation; however, CO dissociation is much more favorable thermodynamically. Furthermore, surfaces with 0.25 monolayer O, OH, and H precoverage promote CO hydrogenation, while they suppress CO oxidation and dissociation. On the surfaces with different CO and H₂O ratios, CO hydrogenation is promoted. On all of these surfaces, COOH formation is not favorable. Considering the reverse reaction, CO₂ dissociation is much favorable kinetically and thermodynamically on all of these surfaces, and CO₂ hydrogenation should be favorable. Finally, metallic iron is not an appropriate catalyst for the water-gas shift reaction

Mechanisms of Mo₂C(101)-Catalyzed Furfural Selective Hydrodeoxygenation to 2‑Methylfuran from Computation

The selective formation of 2-methylfuran (F-CH₃) and furan from furfural (F-CHO) hydrogenation and hydrodeoxygenation on clean and 4H precovered Mo₂C­(101) surfaces has been systematically computed on the basis of periodic density functional theory including dispersion correction (PBE-D3). The clean Mo₂C­(101) surface has two distinct surface sites: unsaturated C and Mo sites for the adsorption of H and furfural, respectively. The selectivity comes from the different preference of furfural hydrogenation and dissociation (F-CHO + H = F-CH₂O vs F-CHO = F-CO + H) under the variation of H₂ partial pressure. On the basis of the computed minimum energy path on the clean surface, microkinetics shows that high H₂ partial pressure can promote 2-methylfuran formation and suppress furan formation. To verify this proposed selectivity trend of 2-methylfuran at high H₂ partial pressure, the 4H precovered Mo₂C­(101) surface (0.25 monolayer hydrogen coverage), which provides neighboring hydrogens for promoting furfural hydrogenation and blocks the active sites for suppressing furfural dissociation, has been used. The computed results are in full agreement with the experimentally observed selective formation of 2-methylfuran and the H₂ reaction order of one half as well as rationalize the need for a high H₂/furfural ratio (400/1). On the basis of these results, a new two-step protocol for experiments is proposed: i.e., the first step is the pretreatment of the catalyst with hydrogen, and the second step is furfural hydrogenation on H precovered catalysts

Formic Acid Dehydrogenation on Ni(111) and Comparison with Pd(111) and Pt(111)

Spin-polarized density functional theory calculations have been performed to investigate formic acid dehydrogenation into carbon dioxide and hydrogen (HCO₂H → CO₂ + H₂) on Ni(111). It is found that formic acid prefers the O (OC) atop adsorption on nickel surface and the H (H–O) atom bridging two neighboring nickel atoms, and formate prefers the bidentate adsorption with O atop on nickel surface. The computed stretching frequencies for deuterated formic acid (DCO₂H) and deuterated formate (DCO₂) on Ni(111) agree well with the experimentally observed IR spectra. Formic acid dehydrogenation into surface formate and hydrogen atom (HCO₂H → HCO₂ + H) has barrier of 0.41 eV and is exothermic by 0.35 eV. Formate dehydrogenation into carbon dioxide and hydrogen atom (HCO₂ → CO₂ + H) has an effective barrier of about 1.0 eV and is the rate-determining step. Our computed adsorption configurations and energetic data for formic acid dehydrogenation on Ni(111) are very close to the reported results for Pt(111), but in sharp contrast to the previously reported results for Pd(111). Our recalculated adsorption configurations and energetic data for formic acid dehydrogenation on Pd(111) are similar to those on Ni(111) and Pt(111), demonstrating the high similarities of these metals. These computed data show that Pd-catalyzed formic acid dehydrogenation has the lowest effective barrier (0.76 eV), followed by Ni (1.03 eV) and Pt (1.56 eV)

Rediscovering the Isospecific Ring-Opening Polymerization of Racemic Propylene Oxide with Dibutylmagnesium

Rediscovering the Isospecific Ring-Opening Polymerization of Racemic Propylene Oxide with Dibutylmagnesiu

Mechanisms of H₂O and CO₂ Formation from Surface Oxygen Reduction on Co(0001)

Surface O removal by H and CO on Co(0001) has been studied using periodic density functional method (revised Perdew–Burke–Ernzerhof ; RPBE) and ab initio atomistic thermodynamics. On the basis of the quantitative agreement in the H₂O formation barrier between experiment (1.34 ± 0.07 eV) and theory (1.32 eV), H₂O formation undergoes a consecutive hydrogenation process [O + 2H → OH + H → H₂O], while the barrier of H₂O formation from OH disproportionation [2OH → H₂O + O] is much lower (0.72 eV). The computed desorption temperatures of H₂ and H₂O under ultrahigh vacuum conditions agree perfectly with the experiment. Surface O removal by CO has a high barrier (1.41 eV) and is strongly endothermic (0.94 eV). Precovered O and OH species do not significantly affect the barriers of H₂O and CO₂ formation. All of these results indicate that the present RPBE method and the larger surface model are more suitable for studying cobalt systems

Synthesis and Catalytic Activity of [Cp′Co(COD)] Complexes Bearing Pendant N‑Containing Groups

The novel Co­(I)-complex [Cp^CNCo­(COD)] (Cp^CN = η⁵-(C₅H₄CMe₂CH₂CN), COD = 1,5-cyclooctadiene; <b>3</b>) with a substituted cyclopentadienyl ligand containing a pendant nitrile moiety has been synthesized and characterized by X-ray diffraction. The reactivity of the nitrile group in <b>3</b> has been investigated regarding its behavior in cyclization reactions with alkynes, leading to three new complexes containing pendant 2-pyridyl groups. All synthesized complexes have been evaluated as catalysts in the [2 + 2 + 2] cycloaddition reaction of 1,6-heptadiyne and benzonitrile

Toward Green Acylation of (Hetero)arenes: Palladium-Catalyzed Carbonylation of Olefins to Ketones

Green Friedel–Crafts acylation reactions belong to the most desired transformations in organic chemistry. The resulting ketones constitute important intermediates, building blocks, and functional molecules in organic synthesis as well as for the chemical industry. Over the past 60 years, advances in this topic have focused on how to make this reaction more economically and environmentally friendly by using green acylating conditions, such as stoichiometric acylations and catalytic homogeneous and heterogeneous acylations. However, currently well-established methodologies for their synthesis either produce significant amounts of waste or proceed under harsh conditions, limiting applications. Here, we present a new protocol for the straightforward and selective introduction of acyl groups into (hetero)­arenes without directing groups by using available olefins with inexpensive CO. In the presence of commercial palladium catalysts, inter- and intramolecular carbonylative C–H functionalizations take place with good regio- and chemoselectivity. Compared to classical Friedel–Crafts chemistry, this novel methodology proceeds under mild reaction conditions. The general applicability of this methodology is demonstrated by the direct carbonylation of industrial feedstocks (ethylene and diisobutene) as well as of natural products (eugenol and safrole). Furthermore, synthetic applications to drug molecules are showcased

Dissociative Hydrogen Adsorption on the Hexagonal Mo₂C Phase at High Coverage

Hydrogen adsorption on the primarily exposed (001), (100), (101), and (201) surfaces of the hexagonal Mo₂C phase at different coverage has been investigated at the level of density functional theory and using ab initio thermodynamics. On the Mo-terminated (001) and (100) as well as mixed Mo/C-terminated (101) and (201) surfaces, dissociative H₂ adsorption is favored both kinetically and thermodynamically. At high coverage, each surface can have several types of adsorption configurations coexisting, and these types are different from surface to surface. The stable coverage as a function of temperature and partial pressure provides useful information not only for surface science studies at ultrahigh vacuum condition but also for practical applications at high temperature and pressure in monitoring reactions. The differences in the adsorbed H atom numbers and energies of these surfaces indicate their different potential hydrotreating abilities. The relationship between surface stability and stable hydrogen coverage has been discussed