Water and Cu Synergy in Selective CO Hydrogenation to Methanol over Cu-MgO-AlO Catalysts.

The CO hydrogenation reaction to produce methanol holds great significance as it contributes to achieving a CO-neutral economy. Previous research identified isolated Cu species doping the oxide surface of a Cu-MgO-AlO-mixed oxide derived from a hydrotalcite precursor as the active site in CO hydrogenation, stabilizing monodentate formate species as a crucial intermediate in methanol synthesis. In this work, we present a molecular-level understanding of how surface water and hydroxyl groups play a crucial role in facilitating spontaneous CO activation at Cu sites and the formation of monodentate formate species.

Vibrational frequencies of CO bound to all three low-index cerium oxide surfaces: A consistent theoretical description of vacancy-induced changes using density functional theory.

The facet-dependent adsorption of CO on oxidized and reduced CeO2 single crystal surfaces is reviewed, with emphasis on the effect of CO coverage and the ability of state-of-the-art quantum-mechanical methods to provide reliable energies and an accurate description of the IR vibrational frequency of CO. Comparison with detailed, high-resolution experimental infrared reflection absorption spectroscopy data obtained for single crystal samples allows the assignment of the different CO vibrational bands observed on all three low-index ceria surfaces. Good agreement is achieved with the hybrid density functional theory approach with the HSE06 functional and with saturation coverage.

Highly Active and Stable Ni/La-Doped Ceria Material for Catalytic CO Reduction by Reverse Water-Gas Shift Reaction.

The design of an active, effective, and economically viable catalyst for CO conversion into value-added products is crucial in the fight against global warming and energy demand. We have developed very efficient catalysts for reverse water-gas shift (rWGS) reaction. Specific conditions of the synthesis by combustion allow the obtention of macroporous materials based on nanosized Ni particles supported on a mixed oxide of high purity and crystallinity.

Shape-Controlled Pathways in the Hydrogen Production from Ethanol Steam Reforming over Ceria Nanoparticles.

The ethanol surface reaction over CeO nanooctahedra (NO) and nanocubes (NC), which mainly expose (111) and (100) surfaces, respectively, was studied by means of infrared spectroscopy (TPSR-IR), mass spectrometry (TPSR-MS), and density functional theory (DFT) calculations. TPSR-MS results show that the production of H is 2.4 times higher on CeO-NC than on CeO-NO, which is rationalized starting from the different types of adsorbed ethoxy species controlled by the shape of the ceria particles.

Tuning Selectivity in the Direct Conversion of Methane to Methanol: Bimetallic Synergistic Effects on the Cleavage of C-H and O-H Bonds over NiCu/CeO Catalysts.

The efficient activation of methane and the simultaneous water dissociation are crucial in many catalytic reactions on oxide-supported transition metal catalysts. On very low-loaded Ni/CeO surfaces, methane easily fully decomposes, CH → C + 4H, and water dissociates, HO→ OH + H. However, in important reactions such as the direct oxidation of methane to methanol (MTM), where complex interplay exists between reactants (CH, O), it is desirable to avoid the complete dehydrogenation of methane to carbon.

Erratum: Vibrational Frequencies of Cerium-Oxide-Bound CO: A Challenge for Conventional DFT Methods [Phys. Rev. Lett. 125, 256101 (2020)].

This corrects the article DOI: 10.1103/PhysRevLett.125.

Nature of the Active Sites on Ni/CeO Catalysts for Methane Conversions.

Effective catalysts for the direct conversion of methane to methanol and for methane's dry reforming to syngas are Holy Grails of catalysis research toward clean energy technologies. It has recently been discovered that Ni at low loadings on CeO(111) is very active for both of these reactions. Revealing the nature of the active sites in such systems is paramount to a rational design of improved catalysts.

Facet-dependent stability of near-surface oxygen vacancies and excess charge localization at CeOsurfaces.

To study the dependence of the relative stability of surface () and subsurface () oxygen vacancies with the crystal facet of CeO, the reduced (100), (110) and (111) surfaces, with two different concentrations of vacancies, were investigated by means of density functional theory (DFT + U) calculations. The results show that the trend in the near-surface vacancy formation energies for comparable vacancy spacings, i.e.

Reaction Pathway for Coke-Free Methane Steam Reforming on a Ni/CeO Catalyst: Active Sites and the Role of Metal-Support Interactions.

Methane steam reforming (MSR) plays a key role in the production of syngas and hydrogen from natural gas. The increasing interest in the use of hydrogen for fuel cell applications demands development of catalysts with high activity at reduced operating temperatures. Ni-based catalysts are promising systems because of their high activity and low cost, but coke formation generally poses a severe problem.

Vibrational Frequencies of Cerium-Oxide-Bound CO: A Challenge for Conventional DFT Methods.

In ceria-based catalysis, the shape of the catalyst particle, which determines the exposed crystal facets, profoundly affects its reactivity. The vibrational frequency of adsorbed carbon monoxide (CO) can be used as a sensitive probe to identify the exposed surface facets, provided reference data on well-defined single crystal surfaces together with a definitive theoretical assignment exist. We investigate the adsorption of CO on the CeO_{2}(110) and (111) surfaces and show that the commonly applied DFT(PBE)+U method does not provide reliable CO vibrational frequencies by comparing with state-of-the-art infrared spectroscopy experiments for monocrystalline CeO_{2} surfaces.

Breaking Simple Scaling Relations through Metal-Oxide Interactions: Understanding Room-Temperature Activation of Methane on M/CeO (M = Pt, Ni, or Co) Interfaces.

The clean activation of methane at low temperatures remains an eminent challenge and a field of competitive research. In particular, on late transition metal surfaces such as Pt(111) or Ni(111), higher temperatures are necessary to activate the hydrocarbon molecule, but a massive deposition of carbon makes the metal surface useless for catalytic activity. However, on very low-loaded M/CeO (M = Pt, Ni, or Co) surfaces, the dissociation of methane occurs at room temperature, which is unexpected considering simple linear scaling relationships.

Direct Conversion of Methane to Methanol on Ni-Ceria Surfaces: Metal-Support Interactions and Water-Enabled Catalytic Conversion by Site Blocking.

The transformation of methane into methanol or higher alcohols at moderate temperature and pressure conditions is of great environmental interest and remains a challenge despite many efforts. Extended surfaces of metallic nickel are inactive for a direct CH → CHOH conversion. This experimental and computational study provides clear evidence that low Ni loadings on a CeO(111) support can perform a direct catalytic cycle for the generation of methanol at low temperature using oxygen and water as reactants, with a higher selectivity than ever reported for ceria-based catalysts.

In Situ Investigation of Methane Dry Reforming on Metal/Ceria(111) Surfaces: Metal-Support Interactions and C-H Bond Activation at Low Temperature.

Studies with a series of metal/ceria(111) (metal=Co, Ni, Cu; ceria=CeO ) surfaces indicate that metal-oxide interactions can play a very important role for the activation of methane and its reforming with CO at relatively low temperatures (600-700 K). Among the systems examined, Co/CeO (111) exhibits the best performance and Cu/CeO (111) has negligible activity. Experiments using ambient pressure X-ray photoelectron spectroscopy indicate that methane dissociates on Co/CeO (111) at temperatures as low as 300 K-generating CH and CO species on the catalyst surface.

Diffusion Barriers Block Defect Occupation on Reduced CeO_{2}(111).

Surface defects are believed to govern the adsorption behavior of reducible oxides. We challenge this perception on the basis of a combined scanning-tunneling-microscopy and density-functional-theory study, addressing the Au adsorption on reduced CeO_{2-x}(111). Despite a clear thermodynamic preference for oxygen vacancies, individual Au atoms were found to bind mostly to regular surface sites.

Dry Reforming of Methane on a Highly-Active Ni-CeO2 Catalyst: Effects of Metal-Support Interactions on C-H Bond Breaking.

Ni-CeO2 is a highly efficient, stable and non-expensive catalyst for methane dry reforming at relative low temperatures (700 K). The active phase of the catalyst consists of small nanoparticles of nickel dispersed on partially reduced ceria. Experiments of ambient pressure XPS indicate that methane dissociates on Ni/CeO2 at temperatures as low as 300 K, generating CHx and COx species on the surface of the catalyst.

Monoxide carbon frequency shift as a tool for the characterization of TiO2 surfaces: insights from first principles spectroscopy.

The adsorption and vibrational frequency of CO on defective and undefective titanium dioxide surfaces is examined applying first-principles molecular dynamics simulations. In particular, the vibrational frequencies are obtained beyond the harmonic approximation, through the time correlation functions of the atomic trajectories. In agreement with experiments, at low CO coverages we find an upshift in the vibration frequency with respect to the free CO molecule, of 45 and 35 cm(-1) on the stoichiometric rutile (110) and anatase (101) faces, respectively.

DFT study of dissociative adsorption of hydrogen sulfide on Cu(111) and Au(111).

Density functional theory (DFT) is used to investigate the reaction pathways for H2S adsorption on Au(111) and Cu(111) at low coverage as well as the full decomposition of H2S on Cu(111). On both surfaces, a weakly bonded molecular state is found with the S atom bond on top sites being molecular adsorption, a nonactivated process. The H-SH dissociation process is endothermic on Au(111), and all reaction pathways present high activation energy barriers which explains the extremely low dissociation probability of H2S on defect-free Au(111) estimated from experiments.

The reaction pathways for HSCH3 adsorption on Au(111): a density functional theory study.

Density functional theory was used to investigate the reaction pathways for HSCH(3) adsorption on Au(111) at low coverage. A molecular adsorbed state was found with the S atom bond on Top sites (E approximately -0.38 eV) and molecular adsorption is nonactivated.

Tuning the nonlocal spin-spin interaction between quantum dots with a magnetic field.

We describe a device where the nonlocal spin-spin interaction between quantum dots (QDs) can be turned on and off with a small magnetic field. The setup consists of two QDs at the edge of two two-dimensional electron gases (2DEGs). The QDs' spins are coupled through a RKKY-like interaction mediated by the electrons in the 2DEGs.