Cu-exchanged Y zeolite was investigated in order to determine the location of the copper cations relative to the zeolite framework and to determine which Cu cations are active for the oxidative carbonylation of methanol to dimethyl carbonate (DMC). Cu-Y zeolite was prepared by vapor-phase exchange of H-Y with CuCl. The oxidation state, local coordination, and bond distances of Al and Cu were determined using Al K-edge and Cu K-edge X-ray absorption spectroscopy (XAS). Complimentary information was obtained by H 2 temperature-programmed reduction and by in-situ infrared spectroscopy. Cu-Y has a Cu/Al ratio of unity and very little occluded CuCl. The average Al-O and Al-Cu bond distances are 1.67 Å and 2.79 Å, respectively, and the average Cu-O and Cu-Si(Al) bond distances are 1.99 Å and 3.13 Å, respectively. All of the Cu exchanged is present as Cu + in sites I′, II, and III′. Cu-Y is active for the oxidative carbonylation of methanol, and at low reactant contact time produces DMC as the primary product. With increasing reactant contact time, DMC formation decreases in preference to the formation of dimethoxy methane (DMM) and methylformate (MF). The formation of DMM and MF is attributed to the hydrogenation of DMC and the hydrogenolysis of DMM, respectively. Observation of the catalyst under reaction conditions reveals that most of the copper cations remain as Cu + , but some oxidation of Cu + to Cu 2+ does occur. It is also concluded that only those copper cations present in site II and III′ positions are accessible to the reactants, and hence are catalytically active. The dominant adsorbed species on the surface are methoxy groups, and adsorbed CO is present as a minority species. The relationship of these observations to the kinetics of DMC synthesis is discussed.

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Aluminum coordination in the framework of USY and ZSM-5 zeolites containing charge-compensating cations (NH4+, H+, or Cu+) was investigated by Al K-edge EXAFS and XANES. This work was performed using a newly developed in-situ cell designed especially for acquiring soft X-ray absorption data. Both tetrahedrally and octahedrally coordinated Al were observed for hydrated H-USY and H-ZSM-5, in good agreement with 27Al NMR analyses. Upon dehydration, water desorbed from the zeolite, and octahedrally coordinated Al was converted progressively to tetrahedrally coordinated Al. These observations confirmed the hypothesis that the interaction of water with Brønsted acid protons can lead to octahedral coordination of Al without loss of Al from the zeolite lattice. When H+ is replaced with NH4+ or Cu+, charge compensating species that absorb less water, less octahedrally coordinated Al was observed. Analysis of Al K-edge EXAFS data indicates that the Al-O bond distance for tetrahedrally coordinated Al in dehydrated USY and ZSM-5 is 1.67 angstroms. Simulation of k3chi(k) for Cu+ exchanged ZSM-5 leads to an estimated distance between Cu+ and framework Al atoms of 2.79 angstroms.

An in-situ cell using "lab-on-a-chip" technologies has been designed and tested for characterization of catalysts and environmental materials using soft X-ray absorption spectroscopy and spectromicroscopy at photon energies above 250 eV. The sample compartment is 1.0 mm in diameter with a gas path length of 0.8 mm to minimize X-ray absorption in the gas phase. The sample compartment can be heated to 533 K by an Al resistive heater and gas flows up to 5.0 cm 3 min -1 can be supplied to the sample compartment through microchannels. The performance of the cell was tested by acquiring Cu L 3 -edge XANES data during the reduction and oxidation of a silica- show that with increasing temperature the Cu(II) peak intensity decreases as the Cu(I) peak intensity increases.

The solid-state ion exchange (SSIE) of H-ZSM-5 by CuCl vapor was investigated with the objective of establishing the effects of the temperature at which exchange is carried out on the level of proton exchange for Cu + , the position of the Cu + cations relative to the zeolite lattice, and the extent of CuCl occlusion in the zeolite pores. After SSIE, the resulting Cu-ZSM-5 was characterized by XRD, 27 Al MAS NMR, infrared spectroscopy, H 2 -TPR, and Cu and Cl K-edge X-ray absorption spectroscopy. Evidence was found for clusters of CuCl, in addition to Cu + cations present at zeolite cation-exchange positions (ZCu). It was also observed that a part of the occluded CuCl is hydrolyzed to Cu 2 O during SSIE. The distribution of ZCu, CuCl, and Cu 2 O was a strong function of the temperature at which cation exchange was carried out. Virtually complete exchange of all Brønsted acid protons for Cu + cations was achieved at a SSIE temperature of 1023 K. No loss of framework Al was observed at this temperature, and only 10% of the copper introduced into the zeolite was occluded as CuCl. The Cu + cations exchanged for Brønsted acid protons are both doubly and triply coordinated to O atoms, with an average Cu-O bond distance of 1.98 Å. Cu EXAFS and Cl XANES indicated that CuCl is occluded in the form of (CuCl) n (n ) 2, 3, 4) clusters in the channels and intersections of the zeolite. With a decrease in the amount of occluded CuCl, the amount of Cu 2 O formed by hydrolysis during SSIE decreases substantially.

A low-temperature grafting approach using two CuI molecular precursors ([CuOSi(O t Bu)3]4 and [CuO t Bu]4) and a high-temperature exchange reaction using CuCl were utilized with a mesoporous silica support (SBA-15) to investigate the effects of catalyst preparation on the nature of copper−support interactions and site speciation. Detailed X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption fine-structure studies (EXAFS) studies were performed to characterize the nature of the Cu sites and the Cu−support interactions. The freshly prepared materials from the nonaqueous grafting of [CuOSi(O t Bu)3]4 (CuOSi/SBA (x.x), where x.x refers to the Cu weight %) exhibit CuI site isolation (by EXAFS and XANES). In contrast, EXAFS and XANES studies of the freshly prepared materials from the nonaqueous grafting of [CuO t Bu]4 (CuO t Bu/SBA (x.x)) suggest that the Cu−O−Cu linkages of the molecular precursor remain intact upon interacting with the support. Isolated CuI sites are observed as the major species in the freshly prepared material from the high-temperature exchange reaction using CuCl (CuCl/SBA (3.0)) (by XANES and EXAFS). Treatment of the materials under He at 573 K leads to loss of the organic species from the grafted materials (by 1H NMR spectroscopy, thermogravimetric analysis, EA, and IR spectroscopy). EXAFS and XANES studies revealed that CuCl/SBA (3.0) and the CuOSi/SBA (x.x) materials still exhibit up to 95% isolated CuI sites, whereas the CuO t Bu/SBA (x.x) materials only exhibit Cu as Cu0 nanoparticles of ca. 7 Å in diameter. After calcination under O2 at 573 K, residual chloride from the high-temperature preparation of CuCl/SBA (3.0) leads to formation of crystalline CuO particles, whereas the CuOSi/SBA (x.x) and CuO t Bu/SBA (x.x) materials exhibit more amorphous CuO character after an identical oxidative treatment.

The partial oxidation of methanol to formaldehyde (FA) was studied over highly dispersed vanadia supported on mesoporous silica SBA-15 (VO x /SBA-15). VO x /SBA-15 catalysts were prepared by a novel grafting/ion-exchange method and characterized using UV-VIS-and Raman spectroscopy. The resulting surface vanadium oxide species (0-2.3 V/nm 2 ), grafted on the inner pores of the SBA-15 silica matrix, consist of tetrahedrally coordinated monomeric and polymeric vanadia. The VO x /SBA-15 catalysts are active and highly selective for the production of FA between 300 and 400°C. Comparison of the reactivity results with literature data reveals that a better catalytic performance can be obtained over vanadia supported on mesoporous silica in comparison with conventional silica samples with the same vanadium loading. Raman characterization of the catalyst after reaction at high conversion indicates that dispersed vanadia partly agglomerates into vanadia crystallites during methanol oxidation.

There is a growing interest in the preparation of catalysts with well-defined and isolated sites, as such systems are ideally suited for structure-function investigations. 1 Recent studies indicate that atomically dispersed metals on high surface area silica materials are effective catalysts. [2][3][4] Thus, an important goal in catalysis research is the development of synthetic methods that provide atomic-level control over the nature of catalytic sites, with formation of isolated single sites or homogeneously distributed and more complicated structures (bimetallic sites, clusters, nanoparticles, etc.) providing new and improved catalysts. [1][2][3][4] It is believed that low-temperature approaches will be most effective for generating tailored structures because of the metastable nature of many of the desired structures. 1 Supported Cu-containing catalysts have been studied for a number of industrially relevant reactions, 5-8 but little effort has been devoted to the generation of tailored sites. The introduction of isolated species onto mesoporous silica using molecular precursors of the form M[OSi(O t Bu) 3 ] n (M ) Ti 3a and Fe 3b ) under nonaqueous conditions has recently been reported. The work presented herein provides direct evidence for atomic-level control over the nature of sites that result from grafting 9 Cu-containing molecular precursors onto the mesoporous silica SBA-15. 10 Reaction of the molecular precursors [CuOSi(O t Bu) 3 ] 4 11 (1) or [CuO t Bu] 4 12 (2) (as solutions in C 6 H 6 ) with the surface hydroxyl groups of SBA-15 under inert conditions provided grafted materials, isolated as light yellow powders after extensive washing with C 6 H 6 and drying in vacuo at 323 K. Quantities of the molecular precursors were used such that the final grafted materials contained ca. 3.5% (CuOSi/SBA(3.5) and CuO t Bu/SBA(3.5) from 1 and 2, respectively) and ca. 5.0% (CuOSi/SBA(5.0) and CuO t Bu/SBA(5.0) from 1 and 2, respectively) Cu by weight. 13 It is known that M[OSi-(O t Bu) 3 ] n species cleanly evolve 3nCH 2 C(CH 3 ) 2 and 3 / 2 nH 2 O upon mild thermolysis (373 to 473 K) to give MSi n O y materials. 1a,14 Previous studies of 1 indicate that it also exhibits loss of CH 2 C-(CH 3 ) 2 and H 2 O upon heating, although some reduction of Cu (to Cu metal) is evident under an inert atmosphere. 11 It was anticipated that grafting 1 onto SBA-15 would provide species that could eliminate CH 2 C(CH 3 ) 2 and H 2 O upon thermolysis to form Si-O surface linkages while maintaining some of the original Cu-OSi linkages to provide stabilized Cu(I) species (in the form of isolated tetramers or as single sites). Use of 2 in similar grafting reactions may also provide isolated sites; however, no additional Si-O surface linkages (and hence extra site stabilization) are provided by this precursor. Scheme 1 illustrates a possible grafting pathway and potential structure types for the resulting surface species.The molecular precursors are presumably well-separated on the surface, as the "OH" site-to-precursor ratios ...