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To understand the metal–support interaction of oxide supported transition metal catalysts, we computed the reaction mechanisms of dry and steam reforming of methane on a tetragonal ZrO2(101) supported Ni catalyst. Based on the limited number of active sites on the surface, an irregular and non-ideal Ni13 cluster on ZrO2(101) is identified as a catalyst. A simple reaction mechanism is proposed, and the first direct dissociation step of CO2, CH4 and H2O is the most difficult based on the computed Gibbs free energies and no surface CHXO and CHXOH intermediates are involved, different from that on the flat Ni(111) surface. Analysis of other supported nickel catalysts shows that not only the support but also the size and shape of the metal clusters play an important role in the reaction mechanisms and kinetics. [ABSTRACT FROM AUTHOR]

Determining the locations and distributions of Al substitution in zeolite-based catalysts and catalysis is always very challenging. Despite advanced experimental characterization techniques and improved theoretical models, this issue is not reasonably solved and this is because the locations and distributions of Al substitution in zeolites are more kinetically than thermodynamically controlled. In this work, we computed one Al substitution in the orthorhombic form of MFI (HZSM-5) which contains 12 distinct tetrahedral (T) centers on the basis of a periodic slab model containing 96 T centers including van der Waals dispersion correction (GGA-PBE-D3). For all 12 T centers, there are 48 acidic sites and each site can be considered for the adsorption of probe molecules. Thermodynamically, the energy span of the twelve most stable acidic sites is less than 15 kJ mol−1, and such a small energy difference enables all adjustable possibilities for the locations and distributions of Al substitution under suitable conditions. Excellent agreement between experiment and theory in the adsorption enthalpies of pyridine, methylamine, dimethylamine and trimethylamine shows that the location of Al substitution is most likely at T1, T3, T5, T7 and T11, while much less likely at the often used T12 site. These results provide the basis for identifying Al substitution in new synthesized HZSM-5 catalysts and for studying the acidic site-dependent catalytic activity of HZSM-5 in cracking and hydrogenation reactions. [ABSTRACT FROM AUTHOR]

The mechanism of coverage dependent CO adsorption and dissociation on the Mo(100) surface was investigated using periodic density functional theory. Structure optimization and frequency calculation were carried out using the GGA-PBE method and a p(3 × 3) supercell model. Energetic data have been obtained using the revised PBE method and the PBE optimized structures. CO adsorption prefers tilted adsorption configuration at the 4-fold hollow sites at low coverage and tilted and atop configurations at high coverage. The computed C–O stretching frequencies of the tilted and atop adsorbed CO molecules agree very well with the experimental results. Starting from the saturation coverage, five binding states have been found: two for molecular (α) CO adsorption and three for dissociative (β) CO adsorption, which are in agreement with the temperature-programmed desorption experiments. In addition, CO prefers dissociation with very low barriers in all coverages as long as free sites are available and is coverage independent; this nicely explains the observed CO dissociation at very low temperatures. All such agreements validate our computational methods and provide the basis of further studies. [ABSTRACT FROM AUTHOR]

Systematic density functional theory calculations and ab initio atomistic thermodynamics were applied to investigate the stability of seven metallic Mo surfaces [(110), (211), (111), (321), (310), (210) (100)] and their coverage dependent hydrogen adsorption. Only dissociative hydrogen adsorption is favored on these surfaces up to more than one monolayer saturation coverage. The computed hydrogen desorption temperatures on Mo(100) at 500 K and on Mo(110) at 410 K are in agreement with the available temperature-programmed desorption results. Under the consideration of H2 as the reduction reagent in Mo catalyst preparation, the computed surface morphology of Mo single crystal shows only exposed (110), (211) and (100) at high temperature; and the estimated surface proportion order of (110) ＞ (211) ＞ (100) agrees very well with the X-ray diffraction detected intensity order of (110) ＞ (211) ＞ (100). Surface reconstruction upon hydrogen adsorption has also been discussed. [ABSTRACT FROM AUTHOR]

The adsorption and co-adsorption of CO and H2 at different coverages on p(4 × 4) Ru(0001) have been computed using periodic density functional theory (GGA-RPBE) and atomistic thermodynamics. Only molecular CO adsorption is possible and the saturation coverage is 0.75 ML (nCO = 12) with CO molecules co-adsorbed at different sites and has a hexagonal adsorption pattern as found by low energy electron diffraction. Only dissociative H2 adsorption is possible and the saturation coverage is 1 ML (nH = 16) with H atoms at face-centered cubic sites. The computed CO and H2 desorption patterns and temperatures agree reasonably with the experiments under ultrahigh vacuum conditions. For CO and H2 co-adsorption (nCO + mH2; n = 1–6 and m = 7, 6, 5, 5, 3, 1), CO pre-coverage affects H adsorption strongly, and each pre-adsorbed CO molecule blocks 2H adsorption sites and H2 does not adsorb on the surface with CO pre-coverage larger than 0.44 ML (nCO = 7); all these are in full agreement with the experiments under ultrahigh vacuum conditions. Our results provide the basis for exploring the mechanisms of catalytic conversion of synthesis gas. [ABSTRACT FROM AUTHOR]

Using density functional theory calculations and ab initio atomistic thermodynamics, H2O adsorption and dissociation on the Fe(110) p(4 × 4) surface at different coverages have been computed. At the lowest coverage, the adsorbed H2O, OH, O and H species can migrate easily on the surface. For (H2O)n adsorption, H2O molecules donating H atoms for H-bonding adsorb more strongly than those accepting H atoms for H-bonding. Monomeric H2O dissociation is favored both thermodynamically and kinetically. On nO pre-covered Fe(110) surfaces (n = 1–8), H2O dissociation is accessible for nO + H2O (n = 1–7) both kinetically and thermodynamically, while H2O desorption instead of dissociation occurs at n = 8. With the increased number of surface O atoms, H2 dissociative adsorption energies vary in a narrow range for n = 1–4 and decrease for n = 5–7, while at n = 8, the surface does not adsorb H2. At low OH coverage (n = 2, 4), OH groups are perpendicularly adsorbed without H-bonding, while for n≥ 6, adsorbed OH groups are linearly arranged and stabilized by H-bonding. The maximal OH coverage (n = 12) is 0.75 ML and the reasonable O coverage (n = 7) is 0.44 ML, in line with the experiment. The calculated desorption temperatures of H2O and H2 agree well with the available experimental data. These results provide fundamental insights into water-involved reactions catalyzed by iron and interaction mechanisms of water interaction with metal surfaces. [ABSTRACT FROM AUTHOR]

Irradiation of a substituted ansa-titanocene(iv) dihydroxido complex with visible light induces Ti–O bond dissociation. In contrast to previous studies on structurally similar unbridged complexes, no side reactions are observed and formation of the Ti(iii) species is highly selective. The formation of OH radicals was proved using a biradicaloid species. [ABSTRACT FROM AUTHOR]

Spin-polarized density functional theory computations have been carried out to study the stable adsorption configurations of Cun (n = 1–7, 13) on Fe and Fe3C surfaces for understanding the initial stages of copper promotion in catalysis. At low coverage, two-dimensional aggregation is more preferred over dispersion and three-dimensional aggregation on the Fe(110) and Fe(100) surfaces as well as the metallic Fe3C(010) surfaces, while dispersion is more favorable over aggregation on the Fe(111) surface. On the Fe3C(001) and Fe3C(100) surfaces with exposed iron and carbon atoms, the adsorbed Cu atoms prefer dispersion at low coverage, while aggregation along the iron regions at high coverage. On the iron surfaces, the adsorption energies of Cun (n = 2–7) are highest on Fe(111), medium on Fe(100) and lowest on Fe(110). On the Fe3C surfaces, the adsorption energies of Cun (n = 1–3) are highest on Fe3C(100), medium on Fe3C(010) and lowest on Fe3C(001), while, for n = 4–7 and 13, Fe3C(010) has stronger adsorption than Fe3C(100). On the basis of their differences in electronegativity, the adsorbed Cu atoms can oxidize the metallic Fe(110), Fe(100) and Fe3C(010) surfaces and become negatively charged. On the Fe3C(001) and Fe3C(100) surfaces with exposed iron and carbon atoms, the adsorbed Cu atoms interacting with surface carbon atoms are oxidized and positively charged. Unlike the most stable Fe(110) and Fe3C(001) surfaces, where the Fe(110) surface has stronger Cu affinity than the Fe3C(001) surface, which is in agreement with the experimental finding, the less and least stable Fe3C(010) and Fe3C(100) surfaces have stronger Cu affinities than the Fe(110) and Fe(100) surfaces. Since less stable facets are not preferably formed thermodynamically, it is crucial to prepare such surfaces to explore Cu adsorption and promotion, and this provides challenges to surface sciences. [ABSTRACT FROM AUTHOR]

To understand the metal-support interaction of oxide supported transition metal catalysts, we computed the reaction mechanisms of dry and steam reforming of methane on a tetragonal ZrO 2 (101) supported Ni catalyst. Based on the limited number of active sites on the surface, an irregular and non-ideal Ni 13 cluster on ZrO 2 (101) is identified as a catalyst. A simple reaction mechanism is proposed, and the first direct dissociation step of CO 2 , CH 4 and H 2 O is the most difficult based on the computed Gibbs free energies and no surface CH X O and CH X OH intermediates are involved, different from that on the flat Ni(111) surface. Analysis of other supported nickel catalysts shows that not only the support but also the size and shape of the metal clusters play an important role in the reaction mechanisms and kinetics.

The development of base metal catalysts for industrially relevant amination and hydrogenation reactions by applying abundant and atom economical reagents continues to be important for the cost-effective and sustainable synthesis of amines which represent highly essential chemicals. In particular, the synthesis of primary amines is of central importance because these compounds serve as key precursors and central intermediates to produce value-added fine and bulk chemicals as well as pharmaceuticals, agrochemicals and materials. Here we report a Ni-triphos complex as the first Ni-based homogeneous catalyst for both reductive amination of carbonyl compounds with ammonia and hydrogenation of nitroarenes to prepare all kinds of primary amines. Remarkably, this Ni-complex enabled the synthesis of functionalized and structurally diverse benzylic, heterocyclic and aliphatic linear and branched primary amines as well as aromatic primary amines starting from inexpensive and easily accessible carbonyl compounds (aldehydes and ketones) and nitroarenes using ammonia and molecular hydrogen. This Ni-catalyzed reductive amination methodology has been applied for the amination of more complex pharmaceuticals and steroid derivatives. Detailed DFT computations have been performed for the Ni-triphos based reductive amination reaction, and they revealed that the overall reaction has an inner-sphere mechanism with H 2 metathesis as the rate-determining step., Competing Interests: The authors declare no competing financial interest., (This journal is © The Royal Society of Chemistry.)

Combining the basin hopping structure searching algorithm and density functional theory, the iron carbide clusters, Fe x C y (x ≤ 8 and y ≤ 8), and clusters with various stoichiometries (Fe 2n C n , Fe 3n C n , Fe n C 2n , Fe n C 3n and Fe n C 4n (n = 1-7), Fe 5n C 2n , and Fe 4n C n (n = 1-5)) are predicted. The stable structures of iron rich carbide clusters are composed of C-C dimers or single C atoms on the surface of the clusters, which are remarkably different from their corresponding bulk structures, where the carbon atoms are atomically distributed in the iron matrix. The most stable carbon rich clusters are highly diverse in topology (bowl, basket, plane, shoe, necklace, etc.) with long carbon chains. The Bader charge analysis shows that the size effect on iron carbide clusters is an electronic tuning. Large carbon-rich clusters appear even under low carbon chemical potentials, whereas small iron-rich clusters are only energetically stable in high carbon chemical potentials, which indicates that changing the carbon chemical potential can tune the morphology (size and stoichiometry) of the iron carbide clusters. These results may help us understand the catalytic activity of iron and iron carbides in reactions such as the Fischer-Tropsch synthesis and the carbon nanotube formation process.

The adsorption and co-adsorption of CO and H2 at different coverages on p(4 × 4) Ru(0001) have been computed using periodic density functional theory (GGA-RPBE) and atomistic thermodynamics. Only molecular CO adsorption is possible and the saturation coverage is 0.75 ML (nCO = 12) with CO molecules co-adsorbed at different sites and has a hexagonal adsorption pattern as found by low energy electron diffraction. Only dissociative H2 adsorption is possible and the saturation coverage is 1 ML (nH = 16) with H atoms at face-centered cubic sites. The computed CO and H2 desorption patterns and temperatures agree reasonably with the experiments under ultrahigh vacuum conditions. For CO and H2 co-adsorption (nCO + mH2; n = 1-6 and m = 7, 6, 5, 5, 3, 1), CO pre-coverage affects H adsorption strongly, and each pre-adsorbed CO molecule blocks 2H adsorption sites and H2 does not adsorb on the surface with CO pre-coverage larger than 0.44 ML (nCO = 7); all these are in full agreement with the experiments under ultrahigh vacuum conditions. Our results provide the basis for exploring the mechanisms of catalytic conversion of synthesis gas.

The adsorption and co-adsorption of CO and H2 at different coverage on the CdI2-antitype metallic Mo2C(001) surface termination have been systematically computed at the level of periodic density functional theory. Only molecular CO adsorption is possible and the monolayer coverage (1 ML) can have 16CO adsorbed at the top sites. Dissociative H2 adsorption is favored thermodynamically and the monolayer coverage (1 ML) can have 16H adsorbed at the hollow sites. Since CO has much stronger adsorption energy than H2, pre-adsorption of CO is possible. CO pre-adsorption strongly affects atomic hydrogen co-adsorption at a high CO/H2 ratio, while hardly affects that at a low CO/H2 ratio. Under ultra-high vacuum conditions (200 K, 10(-12) atm and CO/H2 = 1/1), the most stable adsorbed surface state has CO/H2 = 15/1. Comparison among the metallic terminations of the CdI2-antitype Mo2C(001), eclipsed Mo2C(001) and orthorhombic Mo2C(100) surfaces shows their different CO and hydrogen adsorption as well as activation properties, which reveals that the CdI2-antitype Mo2C(001) surface is least active. These differences come from their surface bonding properties; the CdI2-antitype Mo2C(001) surface is saturated and less metallic, while the eclipsed Mo2C(001) and orthorhombic Mo2C(100) surfaces are unsaturated and more metallic.

Spin-polarized density functional theory computations have been carried out to study the stable adsorption configurations of Cun (n = 1-7, 13) on Fe and Fe3C surfaces for understanding the initial stages of copper promotion in catalysis. At low coverage, two-dimensional aggregation is more preferred over dispersion and three-dimensional aggregation on the Fe(110) and Fe(100) surfaces as well as the metallic Fe3C(010) surfaces, while dispersion is more favorable over aggregation on the Fe(111) surface. On the Fe3C(001) and Fe3C(100) surfaces with exposed iron and carbon atoms, the adsorbed Cu atoms prefer dispersion at low coverage, while aggregation along the iron regions at high coverage. On the iron surfaces, the adsorption energies of Cun (n = 2-7) are highest on Fe(111), medium on Fe(100) and lowest on Fe(110). On the Fe3C surfaces, the adsorption energies of Cun (n = 1-3) are highest on Fe3C(100), medium on Fe3C(010) and lowest on Fe3C(001), while, for n = 4-7 and 13, Fe3C(010) has stronger adsorption than Fe3C(100). On the basis of their differences in electronegativity, the adsorbed Cu atoms can oxidize the metallic Fe(110), Fe(100) and Fe3C(010) surfaces and become negatively charged. On the Fe3C(001) and Fe3C(100) surfaces with exposed iron and carbon atoms, the adsorbed Cu atoms interacting with surface carbon atoms are oxidized and positively charged. Unlike the most stable Fe(110) and Fe3C(001) surfaces, where the Fe(110) surface has stronger Cu affinity than the Fe3C(001) surface, which is in agreement with the experimental finding, the less and least stable Fe3C(010) and Fe3C(100) surfaces have stronger Cu affinities than the Fe(110) and Fe(100) surfaces. Since less stable facets are not preferably formed thermodynamically, it is crucial to prepare such surfaces to explore Cu adsorption and promotion, and this provides challenges to surface sciences.

Bis-cyclopropanated 1,3,5-tricarbonyl compounds were prepared by a sequence of Claisen condensations and cyclopropanations. The optimization of the conditions proved to be very important to suppress retro-Claisen reactions. The conformation of these molecules was studied by experimental and computational methods. The syn/syn;syn/syn conformation is present for all derivatives. It is exclusively present in the case of the derivative containing a phenyl group located at the terminal carbon atom. In most cases, equilibria with other conformers are found.

A variety of functionalized 3,4-benzo-7-hydroxy-2,9-diazabicyclo[3.3.1]non-7-enes were prepared by one-pot cyclizations of 1,3-bis(silyl enol ethers) with quinazolines. The mechanism of the cyclization was studied by B3LYP/6-31G(d) density functional theory computations. The products could be functionalized by Suzuki cross-coupling reactions. The reaction of 1,3-bis(silyl enol ethers) with phthalazine afforded open-chain rather than cyclization products.

The acid-catalyzed condensation of aldehydes and acetamide has been shown to provide a pool of diverse equilibrating species. For the first time, the synthesis of substituted 1-N-acylamino-1,3-butadienes has been accomplished directly in moderate yields upon telomerization of two molecules of aldehyde with one molecule of carboxamide. Detailed spectroscopic and computational investigations establish the favourable formation of all-trans aminodienes under the reaction conditions. Employment thereof as diene building blocks in Diels-Alder reactions allows for the synthesis of carbocyclic molecules with high stereocontrol.