Achieving Atomic Dispersion of Highly Loaded Transition Metals in Small-Pore Zeolite SSZ-13: High-Capacity and High-Efficiency Low-Temperature CO and Passive NOx Adsorbers.

The majority of harmful atmospheric CO and NOx emissions are from vehicle exhausts. Although there has been success addressing NOx emissions at temperatures above 250 °C with selective catalytic reduction technology, emissions during vehicle cold start (when the temperature is below 150 °C), are a major challenge. Herein, we show we can completely eliminate both CO and NOx emissions simultaneously under realistic exhaust flow, using a highly loaded (2 wt %) atomically dispersed palladium in the extra-framework positions of the small-pore chabazite material as a CO and passive NOx adsorber. Until now, atomically dispersed highly loaded (>0.3 wt %) transition-metal/SSZ-13 materials have not been known. We devised a general, simple, and scalable route to prepare such materials for PtII and PdII . Through spectroscopy and materials testing we show that both CO and NOx can be simultaneously completely abated with 100 % efficiency by the formation of mixed carbonyl-nitrosyl palladium complex in chabazite micropore.

Static and Dynamical Structural Investigations of Metal-Oxide Nanocrystals by Powder X-ray Diffraction: Colloidal Tungsten Oxide as a Case Study.

We have developed a general X-ray powder diffraction (XPD) methodology for the simultaneous structural and compositional characterization of inorganic nanomaterials. The approach is validated on colloidal tungsten oxide nanocrystals (WO3-x NCs), as a model polymorphic nanoscale material system. Rod-shaped WO3-x NCs with different crystal structure and stoichiometry are comparatively investigated under an inert atmosphere and after prolonged air exposure. An initial structural model for the as-synthesized NCs is preliminarily identified by means of Rietveld analysis against several reference crystal phases, followed by atomic pair distribution function (PDF) refinement of the best-matching candidates (static analysis). Subtle stoichiometry deviations from the corresponding bulk standards are revealed. NCs exposed to air at room temperature are monitored by XPD measurements at scheduled time intervals. The static PDF analysis is complemented with an investigation into the evolution of the WO3-x NC structure, performed by applying the modulation enhanced diffraction technique to the whole time series of XPD profiles (dynamical analysis). Prolonged contact with ambient air is found to cause an appreciable increase in the static disorder of the O atoms in the WO3-x NC lattice, rather than a variation in stoichiometry. The time behavior of such structural change is identified on the basis of multivariate analysis.

Unravelling the structure of Magnus' pink salt.

A combination of multinuclear ultra-wideline solid-state NMR, powder X-ray diffraction (pXRD), X-ray absorption fine structure experiments, and first principles calculations of platinum magnetic shielding tensors has been employed to reveal the previously unknown crystal structure of Magnus' pink salt (MPS), [Pt(NH3)4][PtCl4], study the isomeric Magnus' green salt (MGS), [Pt(NH3)4][PtCl4], and examine their synthetic precursors K2PtCl4 and Pt(NH3)4Cl2·H2O. A simple synthesis of MPS is detailed which produces relatively pure product in good yield. Broad (195)Pt, (14)N, and (35)Cl SSNMR powder patterns have been acquired using the WURST-CPMG and BRAIN-CP/WURST-CPMG pulse sequences. Experimentally measured and theoretically calculated platinum magnetic shielding tensors are shown to be very sensitive to the types and arrangements of coordinating ligands as well as intermolecular Pt-Pt metallophilic interactions. High-resolution (195)Pt NMR spectra of select regions of the broad (195)Pt powder patterns, in conjunction with an array of (14)N and (35)Cl spectra, reveal clear structural differences between all compounds. Rietveld refinements of synchrotron pXRD patterns, guided by first principles geometry optimization calculations, yield the space group, unit cell parameters, and atomic positions of MPS. The crystal structure has P-1 symmetry and resides in a pseudotetragonal unit cell with a distance of >5.5 Å between Pt sites in the square-planar Pt units. The long Pt-Pt distances and nonparallel orientation of Pt square planes prohibit metallophilic interactions within MPS. The combination of ultra-wideline NMR, pXRD, and computational methods offers much promise for future investigation and characterization of Pt-containing systems.

In situ/operando studies for the production of hydrogen through the water-gas shift on metal oxide catalysts.

In this perspective article, we show how a series of in situ techniques {X-ray diffraction (XRD), pair-distribution-function analysis (PDF), X-ray absorption fine structure (XAFS), environmental transmission electron microscopy (ETEM), infrared spectroscopy (IR), ambient-pressure X-ray photoelectron spectroscopy (AP-XPS)} can be combined to perform detailed studies of the structural, electronic and chemical properties of metal oxide catalysts used for the production of hydrogen through the water-gas shift reaction (WGS, CO + H2O → H2 + CO2). Under reaction conditions most WGS catalysts undergo chemical transformations that drastically modify their composition with respect to that obtained during the synthesis process. Experiments of time-resolved in situ XRD, XAFS, and PDF indicate that the active phase of catalysts which combine Cu, Au or Pt with oxides such as ZnO, CeO2, TiO2, CeOx/TiO2 and Fe2O3 essentially involves nanoparticles of the reduced noble metals. The oxide support undergoes partial reduction and is not a simple spectator, facilitating the dissociation of water and in some cases modifying the chemical properties of the supported metal. Therefore, to optimize the performance of these catalysts one must take into consideration the properties of the metal and oxide phases. IR and AP-XPS have been used to study the reaction mechanism for the WGS on metal oxide catalysts. Data of IR spectroscopy indicate that formate species are not necessarily involved in the main reaction path for the water-gas shift on Cu-, Au- and Pt-based catalysts. Thus, a pure redox mechanism or associative mechanisms that involve either carbonate-like (CO3, HCO3) or carboxyl (HOCO) species should be considered. In the last two decades, there have been tremendous advances in our ability to study catalytic materials under reaction conditions and we are moving towards the major goal of fully understanding how the active sites for the production of hydrogen through the WGS actually work.

Solving the structure of reaction intermediates by time-resolved synchrotron x-ray absorption spectroscopy.

We present a robust data analysis method of time-resolved x-ray absorption spectroscopy experiments suitable for chemical speciation and structure determination of reaction intermediates. Chemical speciation is done by principal component analysis (PCA) of the time-resolved x-ray absorption near-edge structure data. Structural analysis of intermediate phases is done by theoretical modeling of their extended x-ray absorption fine-structure data isolated by PCA. The method is demonstrated using reduction and reoxidation of Cu-doped ceria catalysts where we detected reaction intermediates and measured fine details of the reaction kinetics. This approach can be directly adapted to many time-resolved x-ray spectroscopy experiments where new rapid throughput data collection and analysis methods are needed.

Synthesis, characterization, and photodegradation behavior of single-phase anatase TiO2 materials synthesized from Ti-oxychloride precursors.

Single-phase anatase-TiO2 nanomaterials with a size of ca. 10 nm and variable quantities of anion impurities were prepared using a novel pathway based on the use of amorphous ammonium Ti-oxychloride precursors synthesized using Ti/Cl initial ratios between 1 and 6. The precursor nature and evolution under thermal treatment were studied using chemical analysis, XRD, XPS, DRIFTS, and mass spectrometry. The nature and concentration of anatase-TiO2 materials anion impurities were analyzed by XPS and DRIFTS. It is shown that negatively charged impurities located in substitutional positions of the anatase network are maximized for a sample synthesized using a Ti/Cl 1:1 atomic ratio and are responsible for the elimination of liquid-phase (phenol) and gas-phase (isopropanol or methylcyclohexane) pollutants under sunlight excitation. A link is established among the initial chemical characterization of the precursors, the final morphological, structural, and chemical composition of the oxide materials, and their photochemical properties.

Thermal decomposition of monocalcium aluminate decahydrate (CaAl2O4.10H2O) investigated by in-situ synchrotron X-ray powder diffraction, thermal analysis and 27Al, 2H MAS NMR spectroscopy.

The stability of monocalcium aluminate decahydrate, with the nominal composition CaAl(2)O(4).10H(2)O (CAH(10)), has a decisive role for the strength development and durability of cementitious materials based on high alumina cements. This has prompted an investigation of the thermal transformation of crystalline monocalcium aluminate decahydrate in air to an amorphous phase by in-situ synchrotron X-ray powder diffraction in the temperature range from 25 to 500 degrees C, by DTA/TGA, and (2)H, (27)Al MAS NMR spectroscopy. The decomposition includes the loss of hydrogen-bonded water molecules in the temperature range up to 175 degrees C, coupled with a reduction of the unit cell volume from 1928 A(3) at 25 degrees C, to 1674 A(3) at 185 degrees C. Furthermore, X-ray diffraction shows that CaAl(2)O(4).10H(2)O starts to transform to an amorphous phase at approximately 65 degrees C. This phase is fully developed at approximately 175 degrees C and it converts to crystalline CaAl(2)O(4) when heated to 1300 degrees C. The thermal decomposition in the temperature range from approximately 65 to approximately 175 degrees C involves both formation of an amorphous phase including AlO(4) tetrahedra and structural changes in the remaining crystalline phase.

Formation of Pd/Au nanostructures from Pd nanowires via galvanic replacement reaction.

Bimetallic nanostructures with non-random metal atoms distribution are very important for various applications. To synthesize such structures via benign wet chemistry approach remains challenging. This paper reports a synthesis of a Au/Pd alloy nanostructure through the galvanic replacement reaction between Pd ultrathin nanowires (2.4 +/- 0.2 nm in width, over 30 nm in length) and AuCl3 in toluene. Both morphological and structural changes were monitored during the reaction up to 10 h. Continuous changes of chemical composition and crystalline structure from Pd nanowires to Pd68Au32 and Pd45Au55 alloys, and to Au nanoparticles were observed. More interestingly, by using combined techniques such as high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), energy dispersive X-ray spectrometry (EDS), UV-vis absorption, and extended X-ray absorption fine structure (EXAFS) spectroscopy, we found the formation of Pd68Au32 non-random alloy with Au-rich core and Pd-rich shell, and random Pd45Au55 alloy with uniformly mixed Pd and Au atom inside the nanoparticles, respectively. Density functional theory (DFT) calculations indicated that alkylamine will strongly stabilize Pd to the surface, resulting in diffusion of Au atoms into the core region to form a non-random alloy. We believe such benign synthetic techniques can also enable the large scale preparation of various types of non-random alloys for several technically important catalysis applications.

Structure of calcium aluminate decahydrate (CaAl2O4.10D2O) from neutron and X-ray powder diffraction data.

Calcium aluminate decahydrate is hexagonal with the space group P6(3)/m and Z = 6. The compound has been named CaAl(2)O(4).10H(2)O (CAH(10)) for decades and is known as the product obtained by hydration of CaAl(2)O(4) (CA) in the temperature region 273-288 K - one of the main components in high-alumina cements. The lattice constants depend on the water content. Several sample preparations were used in this investigation: one CAH(10), three CAD(10) and one CA(D/H)(10), where the latter is a zero-matrix sample showing no coherent scattering contribution from the D/H atoms in a neutron diffraction powder pattern. The crystal structure including the positions of the H/D atoms was determined from analyses of four neutron diffraction powder patterns by means of the ab initio crystal structure determination program FOX and the FULLPROF crystal structure refinement program. Additionally, eight X-ray powder diffraction patterns (Cu Kalpha(1) and synchrotron X-rays) were used to establish phase purity. The analyses of these combined neutron and X-ray diffraction data clearly show that the previously published positions of the O atoms in the water molecules are in error. Thermogravimetric analysis of the CAD(10) sample preparation used for the neutron diffraction studies gave the composition CaAl(2)(OD)(8)(D(2)O)(2).2.42D(2)O. Neutron and X-ray powder diffraction data gave the structural formula CaAl(2)(OX)(8)(X(2)O)(2).gammaX(2)O (X = D, H and D/H), where the gamma values are sample dependent and lie between 2.3 and 3.3.

Anatase-TiO2 nanomaterials: analysis of key parameters controlling crystallization.

Nanoparticulated TiO2 materials with anatase structure were synthesized by using a microemulsion method. The structural characteristics of the amorphous solid precursors and their evolution during thermal treatments were studied by using X-ray absorption structure (X-ray absorption near edge structure XANES and extended X-ray absorption fine structure EXAFS), XRD-PDF (X-ray diffraction-pair distribution function), and infrared spectroscopy. Concerning the precursor materials, XANES and EXAFS showed a local order closely related to that of the anatase structure but containing defective, undercoordinated Ti5c4+ species in addition to normal Ti6c4+ species. The PDF technique detects differences among samples in the local order (below 1 nm) and showed that primary particle size varies throughout the amorphous precursor series. The physical interpretation of results concerning the amorphous materials and their evolution under thermal treatment gives conclusive evidence that local, intraparticle ordering variations determine the temperature for the onset of the nucleation process and drive the solid behavior through the whole crystallization process. The significance of this result in the context of current crystallization theories of oxide-based nanocrystalline solids is discussed.

Structures of three dehydration products of bischofite from in situ synchrotron powder diffraction data (MgCl2.nH2O; n = 1, 2, 4).

High-quality in situ synchrotron powder diffraction data have been used to investigate the decomposition products of bischofite in the temperature range 298

In situ synthesis of mixed-valent manganese oxide nanocrystals: an in situ synchrotron X-ray diffraction study.

Phase transformations of materials can be studied by in situ synchrotron X-ray diffraction. However, most reported in situ synchrotron XRD studies focus on solid state/gel systems by measuring phase/structure changes during application of pressure or heat. Phase transformations during material synthesis and their applications, especially in wet chemistry processes with different media, have not drawn much attention. Here, using manganese oxides as examples, we report the successful characterization of phase transformations in in situ hydrothermal synthesis conditions by the in situ synchrotron XRD method using a quartz/sapphire capillary tube as the synthesis reactor. The results were used for better design of materials with controlled structures and properties. This method can be generally used for synthesis of manganese oxides as well as for in situ characterization of other material syntheses using hydrothermal, sol-gel, and other methods. In addition, catalytic processes in liquid-solid, gas-solid, and solid-solid systems can also be studied in such an in situ way so that catalytic mechanisms can be better understood and catalyst synthesis and catalytic processes can be optimized.

In situ studies of the active sites for the water gas shift reaction over Cu-CeO2 catalysts: complex interaction between metallic copper and oxygen vacancies of ceria.

New information about the active sites for the water gas shift (WGS) reaction over Cu-CeO2 systems was obtained using in-situ, time-resolved X-ray diffraction (TR-XRD), X-ray absorption spectroscopy (TR-XAS, Cu K and Ce L3 edges), and infrared spectroscopy (DRIFTS). Cu-CeO2 nanoparticles prepared by a novel reversed microemulsion method (doped Ce1-xCuxO2 sample) and an impregnation method (impregnated CuOx/CeO2 sample) were studied. The results from all of the samples indicate that both metallic copper and oxygen vacancies in ceria were involved in the generation of active sites for the WGS reaction. Evidence was found for a synergistic Cu-Ovacancy interaction. This interaction enhances the chemical activity of Cu, and the presence of Cu facilitates the formation of O vacancies in ceria under reaction conditions. Water dissociation occurred on the Ovacancy sites or the Cu-Ovacancy interface. No significant amounts of formate were formed on the catalysts during the WGS reaction. The presence of strongly bound carbonates is an important factor for the deactivation of the catalysts at high temperatures. This work identifies for the first time the active sites for the WGS reaction on Cu-CeO2 catalysts and illustrates the importance of in situ structural studies for heterogeneous catalytic reactions.

The structural and electronic properties of nanostructured Ce1-x-yZrxTbyO2 ternary oxides: unusual concentration of Tb3+ and metal<-->oxygen<-->metal interactions.

Ceria-based ternary oxides are widely used in many areas of chemistry, physics, and materials science. Synchrotron-based time-resolved x-ray diffraction, x-ray absorption near-edge spectroscopy (XANES), Raman spectroscopy, and density-functional calculations were used to study the structural and electronic properties of Ce-Zr-Tb oxide nanoparticles. The nanoparticles were synthesized following a novel microemulsion method and had sizes in the range of 4-7 nm. The Ce1-x-yZrxTbyO2 ternary systems exhibit a complex behavior that cannot be predicted as a simple extrapolation of the properties of Ce1-xZrxO2, Ce1-xTbxO2, or the individual oxides (CeO2, ZrO2, and TbO2). The doping of ceria with Zr and Tb induces a decrease in the unit cell, but there are large positive deviations with respect to the cell parameters predicted by Vegard's rule for ideal solid solutions. The presence of Zr and Tb generates strain in the ceria lattice through the creation of crystal imperfections and O vacancies. The O K-edge and Tb LIII-edge XANES spectra for the Ce1-x-yZrxTbyO2 nanoparticles point to the existence of distinctive electronic properties. In Ce1-x-yZrxTbyO2 there is an unexpected high concentration of Tb3+, which is not seen in TbO2 or Ce1-xTbxO2 and enhances the chemical reactivity of the ternary oxide. Tb<-->O<-->Zr interactions produce a stabilization of the Tb(4f,5d) states that is responsible for the high concentration of Tb(3+) cations. The behavior of Ce1-x-yZrxTbyO2 illustrates how important can be metal<-->oxygen<-->metal interactions for determining the structural, electronic, and chemical properties of a ternary oxide.

Unusual physical and chemical properties of Cu in Ce(1-x)Cu(x)O(2) oxides.

The structural and electronic properties of Ce(1-x)Cu(x)O(2) nano systems prepared by a reverse microemulsion method were characterized with synchrotron-based X-ray diffraction, X-ray absorption spectroscopy, Raman spectroscopy, and density functional calculations. The Cu atoms embedded in ceria had an oxidation state higher than those of the cations in Cu(2)O or CuO. The lattice of the Ce(1)(-x)Cu(x)O(2) systems still adopted a fluorite-type structure, but it was highly distorted with multiple cation-oxygen distances with respect to the single cation-oxygen bond distance seen in pure ceria. The doping of CeO(2) with copper introduced a large strain into the oxide lattice and favored the formation of O vacancies, leading to a Ce(1-x)Cu(x)O(2-y) stoichiometry for our materials. Cu approached the planar geometry characteristic of Cu(II) oxides, but with a strongly perturbed local order. The chemical activities of the Ce(1-x)Cu(x)O(2) nanoparticles were tested using the reactions with H(2) and O(2) as probes. During the reduction in hydrogen, an induction time was observed and became shorter after raising the reaction temperature. The fraction of copper that could be reduced in the Ce(1-x)Cu(x)O(2) oxides also depended strongly on the reaction temperature. A comparison with data for the reduction of pure copper oxides indicated that the copper embedded in ceria was much more difficult to reduce. The reduction of the Ce(1-x)Cu(x)O(2) nanoparticles was rather reversible, without the generation of a significant amount of CuO or Cu(2)O phases during reoxidation. This reversible process demonstrates the unusual structural and chemical properties of the Cu-doped ceria materials.

Crystal structures and topological aspects of the high-temperature phases and decomposition products of the alkali-metal oxalates M2[C2O4] (M=K, Rb, Cs).

The high-temperature phases of the alkali-metal oxalates M2[C2O4] (M = K, Rb, Cs), and their decomposition products M2[CO3] (M = K, Rb, Cs), were investigated by fast, angle-dispersive X-ray powder diffraction with an image-plate detector, and also by simultaneous differential thermal analysis (DTA)/thermogravimetric analysis (TGA)/mass spectrometry (MS) and differential scanning calorimetry (DSC) techniques. The following phases, in order of decreasing temperature, were observed and crystallographically characterized (an asterisk denotes a previously unknown modification): *alpha-K2[C2O4], *alpha-Rb2[C2O4], *alpha-Cs2[C2O4], alpha-K2[CO3], *alpha-Rb2[CO3], and *alpha-Cs2[CO3] in space group P6(3)/mmc; *beta-Rb2[C2O4], *beta-Cs2[C2O4], *beta-Rb2[CO3], and *beta-Cs2[CO3] in Pnma; gamma-Rb2[C2O4], gamma-Cs[C2O4], gamma-Rb2[CO3], and gamma-Cs2[CO3] in P2(1)/c; and delta-K2[C2O4] and delta-Rb2[C2O4] in Pbam. With respect to the centers of gravity of the oxalate and carbonate anions, respectively, the crystal structures of all known alkali-metal oxalates and carbonates belong to the AlB2 family, and adopt either the AlB2 or the Ni2In arrangement depending on the size of the cation and the temperature. Despite the different sizes and constitutions of the carbonate and oxalate anions, the high-temperature phases of the alkali-metal carbonates M2[CO3] (M = K, Rb, Cs), exhibit the same sequence of basic structures as the corresponding alkali-metal oxalates. The topological aspects and order-disorder phenomena at elevated temperature are discussed.

The behavior of mixed-metal oxides: physical and chemical properties of bulk Ce1-xTbxO2 and nanoparticles of Ce1-xTbxOy.

The physical and chemical properties of bulk Ce(1-x)Tb(x)O(2) and Ce(1-x)Tb(x)O(y) nanoparticles (xTb exchange nor the introduction of oxygen vacancies in Ce(1-x)Tb(x)O(y) significantly affect the charge on the Ce cations. In contrast, the O K-edge and Tb L(III)-edge XANES spectra for Ce(1-x)Tb(x)O(y) nanoparticles show substantial changes with respect to the corresponding spectra of Ce and Tb single oxide references. The Ce(0.5)Tb(0.5)O(y) compounds exhibit a much larger Tb(3+)/Tb(4+) ratio than TbO(1.7). A comparison with the properties of Ce(1-x)Zr(x)O(y) and Ce(1-x)Ca(x)O(y) shows important differences in the charge distribution, the magnitude of the dopant induced strain in the oxide lattice, and a superior behavior in the case of the Ce(1-x)Tb(x)O(y) systems. The Tb-containing oxides combine stability at high temperature against phase segregation and a reasonable concentration of O vacancies, making them attractive for chemical and catalytic applications.

Structure and reactivity of Ru nanoparticles supported on modified graphite surfaces: a study of the model catalysts for ammonia synthesis.

Supported ruthenium metal catalysts have higher activity than traditional iron-based catalysts used industrially for ammonia synthesis. A study of a model Ru/C catalyst was carried out to advance the understanding of structure and reactivity correlations in this structure-sensitive reaction where dinitrogen dissociation is the rate-limiting step. Ru particles were grown by chemical vapor deposition (CVD) via a Ru(3)(CO)(12) precursor on a highly oriented pyrolytic graphite (HOPG) surface modified with one-atomic-layer-deep holes mimicking activated carbon support. Scanning tunneling microscopy (STM) has been used to investigate the growth, structure, and morphology of the Ru particles. Thermal desorption of dissociatively adsorbed nitrogen has been used to evaluate the reactivity of the Ru/HOPG model catalysts. Two different Ru particle structures with different reactivities to N(2) dissociation have been identified. The initial sticking coefficient for N(2) dissociative adsorption on the Ru/HOPG model catalysts is approximately 10(-6), 4 orders larger compared to that of Ru single-crystal surfaces.

Probing local and long-range structure simultaneously: an in situ study of the high-temperature phase transition of alpha-AlF3.

We show in this Communication that the combination of Rietveld and pair distribution function (PDF) analyses allows unique insight into the nature and driving force of the phase transition of alpha-AlF3, which was not available from conventional structural analysis methods alone. The use of image plate technology allows structural changes to be followed in "real time" and reduces the time required to collect high-resolution PDF data from hours (with a conventional solid state detector) to seconds. This methodology produces raw data that can simultaneously be analyzed by both Rietveld and PDF analysis.