A strategy for high ethylene polymerization performance using titanium single-site catalysts.

The synthesis of heterogeneous Ti(IV)-based catalysts for ethylene polymerization following surface organometallic chemistry concepts is described. The unique feature of this catalyst arises from the silica support, KCC-1. It has (i) a 3D fibrous morphology that is essential to improve the diffusion of the reactants, and (ii) an aluminum-bound hydroxyl group, [(Si-O-Si)(Si-O-)Al-OH] 2, used as an anchoring site.

Atomically Dispersed NiN Site with High Oxygen Electrocatalysis Performance Facilely Produced via a Surface Immobilization Strategy.

Nonprecious-metal heterogeneous catalysts with atomically dispersed active sites demonstrated high activity and selectivity in different reactions, and the rational design and large-scale preparation of such catalysts are of great interest but remain a huge challenge. Current approaches usually involve extremely high-temperature and tedious procedures. Here, we demonstrated a straightforward and scalable preparation strategy.

[Ag(1,2-BDT)]: How Square-Pyramidal Building Blocks Self-Assemble into the Smallest Silver Nanocluster.

The emerging promise of few-atom metal catalysts has driven the need for developing metal nanoclusters (NCs) with ultrasmall core size. However, the preparation of metal NCs with single-digit metallic atoms and atomic precision is a major challenge for materials chemists, particularly for Ag, where the structure of such NCs remains unknown. In this study, we developed a shape-controlled synthesis strategy based on an isomeric dithiol ligand to yield the smallest crystallized Ag NC to date: [Ag(1,2-BDT)] (1,2-BDT = 1,2-benzenedithiolate).

Titanium methyl tamed on silica: synthesis of a well-defined pre-catalyst for hydrogenolysis of n-alkane.

Alkylation of Ti(CH)Cl1 by MeLi gives the homoleptic Ti(CH)2 for the first time in the absence of any coordinating solvent. The reaction of 2 with silica pretreated at 700 °C (SiO) gives two inequivalent silica-supported Ti-methyl species 3. Complex 3 was characterized by IR, microanalysis (ICP-OES, CHNS, and gas quantification), and advanced solid-state NMR spectroscopy (H, C, DQ, TQ, and HETCOR).

Extension of Surface Organometallic Chemistry to Metal-Organic Frameworks: Development of a Well-Defined Single Site [(≡Zr-O-)W(═O)(CHBu)] Olefin Metathesis Catalyst.

We report here the first step by step anchoring of a W(≡CBu)(CHBu) complex on a highly crystalline and mesoporous MOF, namely Zr-NU-1000, using a Surface Organometallic Chemistry (SOMC) concept and methodology. SOMC allowed us to selectively graft the complex on the Zr clusters and characterize the obtained single site material using state of the art experimental methods including extensive solid-state NMR techniques and HAADF-STEM imaging. Further FT-IR spectroscopy revealed the presence of a W═O moiety arising from the in situ reaction of the W≡CBu functionality with the coordinated water coming from the 8-connected hexanuclear Zr clusters.

Designing an active TaN photocatalyst for H and O evolution reactions by specific exposed facet engineering: a first-principles study.

The effects of native defects and exposed facets on the thermodynamic stability and photocatalytic characteristics of Ta3N5 for water splitting are studied by applying accurate quantum computations on the basis of density functional theory (DFT) with the range-separated hybrid functional (HSE06). Among the three explored potential candidates for O-enriched bulk Ta3N5 structures with substituted O at N sites and accompanied by interstitial O or Ta-vacancies, the first and third structures are relevant. The four possible (001), (010), (100) and (110) low Miller index exposed facets of Ta(3-x)N(5-y)Oy (y = 7x) are also explored, which show lower formation energies than those of Ta3N5.

Ligand-free gold nanoclusters confined in mesoporous silica nanoparticles for styrene epoxidation.

We present a novel approach to produce gold nanoclusters (Au NCs) in the pores of mesoporous silica nanoparticles (MSNs) by sequential and controlled addition of metal ions and reducing agents. This impregnation technique was followed to confine Au NCs inside the pores of MSNs without adding external ligands or stabilizing agents. TEM images show a uniform distribution of monodisperse NCs with an average size of 1.

Docking of tetra-methyl zirconium to the surface of silica: a well-defined pre-catalyst for conversion of CO to cyclic carbonates.

The metal complex (Zr(CH3)4(THF)2) has been fully synthesized, characterized and grafted onto partially dehydroxylated silica to give two surface species [([triple bond, length as m-dash]Si-O-)Zr(CH3)3(THF)2] (minor) and [([triple bond, length as m-dash]Si-O-)2Zr(CH3)2(THF)2] (major) which have been characterized by SS NMR, IR, and elemental analysis. These supported pre-catalysts exhibit the best conversion of CO2 to cyclic carbonates, as compared to the previously reported SOMC catalysts.

Imine Metathesis by Silica-Supported Catalysts Using the Methodology of Surface Organometallic Chemistry.

With this protocol, a well-defined singlesite silica-supported heterogeneous catalyst [(≡Si-O-)Hf(=NMe)(η-NMe2)] is designed and prepared according to the methodology developed by surface organometallic chemistry (SOMC). In this framework, catalytic cycles can be determined by isolating crucial intermediates. All air-sensitive materials are handled under inert atmosphere (using gloveboxes or a Schlenk line) or high vacuum lines (HVLs, <10 mbar).

TiO-supported Pt single atoms by surface organometallic chemistry for photocatalytic hydrogen evolution.

A platinum complex, (CH)Pt(COD), is grafted via surface organometallic chemistry (SOMC) on morphology-controlled anatase TiO to generate single, isolated Pt atoms on TiO nano-platelets. The resulting material is characterized by FT-IR, high resolution scanning transmission electron microscopy (HRSTEM), NMR, and XAS, and then used to perform photocatalytic water splitting. The photocatalyst with SOMC-grafted Pt shows superior performance in photocatalytic hydrogen evolution and strongly suppresses the backwards reaction of H and O forming HO under dark conditions, compared to the photocatalyst prepared by impregnation at the same Pt loading.

The Comparison between Single Atom Catalysis and Surface Organometallic Catalysis.

Single atom catalysis (SAC) is a recent discipline of heterogeneous catalysis for which a single atom on a surface is able to carry out various catalytic reactions. A kind of revolution in heterogeneous catalysis by metals for which it was assumed that specific sites or defects of a nanoparticle were necessary to activate substrates in catalytic reactions. In another extreme of the spectrum, surface organometallic chemistry (SOMC), and, by extension, surface organometallic catalysis (SOMCat), have demonstrated that single atoms on a surface, but this time with specific ligands, could lead to a more predictive approach in heterogeneous catalysis.

Defect engineering of metal-oxide interface for proximity of photooxidation and photoreduction.

Close proximity between different catalytic sites is crucial for accelerating or even enabling many important catalytic reactions. Photooxidation and photoreduction in photocatalysis are generally separated from each other, which arises from the hole-electron separation on photocatalyst surface. Here, we show with widely studied photocatalyst Pt/[Formula: see text] as a model, that concentrating abundant oxygen vacancies only at the metal-oxide interface can locate hole-driven oxidation sites in proximity to electron-driven reduction sites for triggering unusual reactions.

A strategy to convert propane to aromatics (BTX) using TiNp grafted at the periphery of ZSM-5 by surface organometallic chemistry.

The direct conversion of propane into aromatics (BTX) using modified ZSM-5 was achieved with a strategy of "catalysis by design". In contrast to the classical mode of action of classical aromatization catalysts which are purely based on acidity, we have designed the catalyst associating two functions: One function (Ti-hydride) was selected to activate the C-H bond of propane by σ-bond metathesis to further obtain olefin by β-H elimination and the other function (Brønsted acid) being responsible for the oligomerization, cyclization, and aromatization. This bifunctional catalyst was obtained by selectively grafting a bulky organometallic complex of tetrakis(neopentyl)titanium (TiNp4) at the external surface (external silanol ([triple bond, length as m-dash]Si-OH) group) of [H-ZSM-5300] to obtain [Ti/ZSM-5] catalyst 1.

Single-Site Molybdenum on Solid Support Materials for Catalytic Hydrogenation of N -into-NH.

Very stable in operando and low-loaded atomic molybdenum on solid-support materials have been prepared and tested to be catalytically active for N -into-NH hydrogenation. Ammonia synthesis is reported at atmospheric pressure and 400 °C with NH rates of approximately 1.3×10  μmol h  g using a well-defined Mo-hydride grafted on silica (SiO ).

Surface organometallic chemistry in heterogeneous catalysis.

The broad challenges of energy and environment have become a main focus of research efforts to develop more active and selective catalytic systems for key chemical transformations. Surface organometallic chemistry (SOMC) is an established concept, associated with specific tools, for the design, preparation and characterization of well-defined single-site catalysts. The objective is to enter a catalytic cycle through a presumed catalytic intermediate prepared from organometallic or coordination compounds to generate well defined surface organometallic fragments (SOMFs) or surface coordination fragments (SCFs).

Predicting the DNP-SENS efficiency in reactive heterogeneous catalysts from hydrophilicity.

Identification of surfaces at the molecular level has benefited from progress in dynamic nuclear polarization surface enhanced NMR spectroscopy (DNP SENS). However, the technique is limited when using highly sensitive heterogeneous catalysts due to secondary reaction of surface organometallic fragments (SOMFs) with stable radical polarization agents. Here, we observe that in non-porous silica nanoparticles (NPs) ( = 15 nm) some DNP enhanced NMR or SENS characterizations are possible, depending on the metal-loading of the SOMF and the type of SOMF substituents (methyl, isobutyl, neopentyl).

SOMC grafting of vanadium oxytriisopropoxide (VO(O Pr)) on dehydroxylated silica; analysis of surface complexes and thermal restructuring mechanism.

Vanadium oxytriisopropoxide (VO(O Pr)), 1, was grafted on highly dehydroxylated silica (SiO: aerosil silica treated at 700 °C under high vacuum) to generate compound 2 following the concepts and methodology of surface organometallic chemistry (SOMC). The resulting compound was analyzed by elemental analysis, FT-IR, H, C and V solid state (SS) NMR, Raman and EPR spectroscopies. The grafting reaction of 1 to generate 2 was found to lead to the formation of a monopodal surface complex [([triple bond, length as m-dash]Si-O-)V(O)(O Pr)], 2m, as well as bipodal [([triple bond, length as m-dash]Si-O-)V(O)(O Pr)], 2b, formed along with ([triple bond, length as m-dash]Si-O- Pr) moieties as an effect of the classical rearrangement of 2m with strained siloxane bridges.

Exploiting the interactions between the ruthenium Hoveyda-Grubbs catalyst and Al-modified mesoporous silica: the case of SBA15 KCC-1.

Immobilization of the 2 generation Hoveyda-Grubbs catalyst onto well-ordered 2D hexagonal (SBA15) and 3D fibrous (KCC-1) mesostructured silica, which contained tetra-coordinated Al, has been investigated through the Surface Organometallic Chemistry (SOMC) methodology. The main interest of this study lies in the peculiarity of the silica supports, which display a well-defined tetrahedral aluminum hydride site displaying a strong Lewis acid character, [([triple bond, length half m-dash]Si-O-Si[triple bond, length half m-dash])([triple bond, length half m-dash]Si-O-)Al-H]. The resulting supported Hoveyda-Grubbs catalysts have been fully characterized by advanced solid state characterization techniques (FT-IR, H and C solid state NMR, DNP-SENS, EF-TEM…).

Morphology control of anatase TiO for well-defined surface chemistry.

A specific allotrope of titanium dioxide (anatase) was synthesized both with a standard thermodynamic morphology ({101}-anatase) and with a highly anisotropic morphology ({001}-anatase) dominated by the {001} facet (81%). The surface chemistry of both samples after dehydroxylation was studied by 1H NMR and FT-IR. The influence of surface fluorides on the surface chemistry was also studied by 1H NMR, FT-IR and DFT.

Ni-Sn-Supported ZrO Catalysts Modified by Indium for Selective CO Hydrogenation to Methanol.

Ni and NiSn supported on zirconia (ZrO) and on indium (In)-incorporated zirconia (InZrO) catalysts were prepared by a wet chemical reduction route and tested for hydrogenation of CO to methanol in a fixed-bed isothermal flow reactor at 250 °C. The mono-metallic Ni (5%Ni/ZrO) catalysts showed a very high selectivity for methane (99%) during CO hydrogenation. Introduction of Sn to this material with the following formulation 5Ni5Sn/ZrO (5% Ni-5% Sn/ZrO) showed the rate of methanol formation to be 0.

A new high temperature reactor for operando XAS: Application for the dry reforming of methane over Ni/ZrO catalyst.

The construction of a high-temperature reaction cell for operando X-ray absorption spectroscopy characterization is reported. A dedicated cell was designed to operate as a plug-flow reactor using powder samples requiring gas flow and thermal treatment at high temperatures. The cell was successfully used in the reaction of dry reforming of methane (DRM).

Clean chlorination of silica surfaces by a single-site substitution approach.

A chlorination method for the selective substitution of well-defined isolated silanol groups of the silica surface has been developed using the catalytic Appel reaction. Spectroscopic analysis, complemented by elemental microanalysis studies, reveals that a quantitative chlorination could be achieved with highly dehydroxylated silica materials that exclusively possess non-hydrogen bonded silanol groups. The employed method did not leave any carbon or phosphorus residue on the silica surface and can be regarded as a promising tool for the future functionalization of metal oxide surfaces.

From single-site tantalum complexes to nanoparticles of Ta N and TaO N supported on silica: elucidation of synthesis chemistry by dynamic nuclear polarization surface enhanced NMR spectroscopy and X-ray absorption spectroscopy.

Air-stable catalysts consisting of tantalum nitride nanoparticles represented as a mixture of Ta N and TaO N with diameters in the range of 0.5 to 3 nm supported on highly dehydroxylated silica were synthesized from TaMe (Me = methyl) and dimeric Ta(OMe) with guidance by the principles of surface organometallic chemistry (SOMC). Characterization of the supported precursors and the supported nanoparticles formed from them was carried out by IR, NMR, UV-Vis, extended X-ray absorption fine structure, and X-ray photoelectron spectroscopies complemented with XRD and high-resolution TEM, with dynamic nuclear polarization surface enhanced NMR spectroscopy being especially helpful by providing enhanced intensities of the signals of H, C, Si, and N at their natural abundances.

Well-defined silica supported bipodal molybdenum oxo alkyl complexes: a model of the active sites of industrial olefin metathesis catalysts.

A well-defined, silica-supported molybdenum oxo alkyl species, ([triple bond, length as m-dash]SiO-)Mo([double bond, length as m-dash]O)(CHBu), was prepared by the selective grafting of Mo([double bond, length as m-dash]O)(CHBu)Cl onto a silica partially dehydroxylated at 200 °C using a rigorous surface organometallic chemistry approach. The immobilized bipodal surface species, partly resembling the active species of industrial MoO/SiO olefin metathesis catalysts, exhibited excellent functional group tolerance in conjunction with its high activity in homocoupling, self and ring closing olefin metathesis.