Facet-dependent diversity of Pt-O coordination for Pt 1 /CeO 2 catalysts achieved by oriented atomic deposition.

The surface chemistry of CeO2 is dictated by the well-defined facets, which exert great influence on the supported metal species and the catalytic performance. Here we report Pt1/CeO2 catalysts exhibiting specific structures of Pt-O coordination on different facets by using adequate preparation methods. The simple impregnation method results in Pt-O3 coordination on the predominantly exposed {111} facets, while the photo-deposition method achieves oriented atomic deposition for Pt-O4 coordination into the "nano-pocket" structure of {100} facets at the top. Compared to the impregnated Pt1/CeO2 catalyst showing normal redox properties and low-temperature activity for CO oxidation, the photo-deposited Pt1/CeO2 exhibits uncustomary strong metal-support interaction and extraordinary high-temperature stability. The preparation methods dictate the facet-dependent diversity of Pt-O coordination, resulting in the further activity-selectivity trade-off. By applying specific preparation routes, our work provides an example of disentangling the effects of support facets and coordination environments for nano-catalysts.

Promoting Molecular Exchange on Rare-Earth Oxycarbonate Surfaces to Catalyze the Water-Gas Shift Reaction.

It is highly desirable to fabricate an accessible catalyst surface that can efficiently activate reactants and desorb products to promote the local surface reaction equilibrium in heterogeneous catalysis. Herein, rare-earth oxycarbonates (Ln2O2CO3, where Ln = La and Sm), which have molecular-exchangeable (H2O and CO2) surface structures according to the ordered layered arrangement of Ln2O22+ and CO32- ions, are unearthed. On this basis, a series of Ln2O2CO3-supported Cu catalysts are prepared through the deposition precipitation method, which provides excellent catalytic activity and stability for the water-gas shift (WGS) reaction. Density functional theory calculations combined with systematic experimental characterizations verify that H2O spontaneously dissociates on the surface of Ln2O2CO3 to form hydroxyl by eliminating the carbonate through the release of CO2. This interchange efficiently promotes the WGS reaction equilibrium shift on the local surface and prevents the carbonate accumulation from hindering the active sites. The discovery of the unique layered structure provides a so-called "self-cleaning" active surface for the WGS reaction and opens new perspectives about the application of rare-earth oxycarbonate nanomaterials in C1 chemistry.

In Situ Generation of the Surface Oxygen Vacancies in a Copper-Ceria Catalyst for the Water-Gas Shift Reaction.

The dissociation of H2O is a crucial aspect for the water-gas shift reaction, which often occurs on the vacancies of a reducible oxide support. However, the vacancies sometimes run off, thus inhibiting H2O dissociation. After high-temperature treatment, the ceria supports were lacking vacancies because of sintering. Unexpectedly, the in situ generation of surface oxygen vacancies was observed, ensuring the efficient dissociation of H2O. Due to the surface reconstruction of ceria nanorods, the copper species sustained were highly dispersed on the sintered support, on which CO was adsorbed efficiently to react with hydroxyls from H2O dissociation. In contrast, no surface reconstruction occurred in ceria nanoparticles, leading to the sintering of copper species. The sintered copper species were averse to adsorb CO, so the copper-ceria nanoparticle catalyst had poor reactivity even when surface oxygen vacancies could be generated in situ.

The Effect of Hydrogenated TiO2 to the Au/TiO2 Catalyst in Catalyzing CO Oxidation.

Supported Au catalysts are widely used for CO oxidation due to their extremely high activity, and the modification of a support structure is a crucial method to improve catalytic performance. Herein, we prepared gold catalysts supported on flaky TiO2 and on TiO2 hydrogenated at different temperatures (200, 400, and 600 °C). We found that the sample with the support pretreated in hydrogen at 600 °C (0.5Au/TiO2-H600) showed the greatest advantages in activity and stability over the sample with as-prepared TiO2 nanosheets (0.5Au/TiO2-UC). First, calcination at 600 °C changed the exposed surface of TiO2 from {001} to {101}, and gold nanoparticles (2-3 nm) were observed as highly reactive species on 0.5Au/TiO2-H600. Moreover, the increase of oxygen vacancies on the surface of 0.5Au/TiO2-H600 was conducive to oxygen activation and promoted the catalytic activity. Therefore, we emphasized the important role of the support and gave an effective method to improve the catalytic performance by regulating the support structure.

Facile Fabrication of CeO2-Al2O3 Hollow Sphere with Atomically Dispersed Fe via Spray Pyrolysis.

A facile spray pyrolysis method is introduced to construct the hollow CeO2-Al2O3 spheres with atomically dispersed Fe. Only nitrates and ethanol were involved during the one-step preparation process using the ultrasound spray pyrolysis approach. Detailed explorations demonstrated that differences in the pyrolysis temperature of the precursors and heat transfer are crucial to the formation of the hollow nanostructure. In addition, iron species were in situ atomically dispersed on the as-formed CeO2-Al2O3 hollow spheres via this strategy, which demonstrated promising potential in transferring syn-gas to valuable gasoline products.

Intrinsically Active Surface in a Pt/γ-Mo2N Catalyst for the Water-Gas Shift Reaction: Molybdenum Nitride or Molybdenum Oxide?

Apart from active metals, supports also contribute significantly to the catalytic performance of supported metal catalysts. On account of the formed strain and defects, the heterostructured surface of the support may play a crucial role to activate the reactant molecules, while it is usually neglected. In this work, the Pt/γ-Mo2N catalyst was prepared via a facile solution method. This Pt/γ-Mo2N catalyst showed excellent activity and stability for catalyzing the water-gas shift (WGS) reaction. The reaction rates at 240 °C were 16.5 molCO molPt-1s-1 in product-free gas and 5.36 molCO molPt-1 s-1 in full reformate gas, which were almost 20 times that of the catalysts reported. It is found that the molybdenum species in the surface of the Pt/γ-Mo2N catalyst is molybdenum oxide as MoO3. This surface MoO3 is very easily reduced even at room temperature, and it transformed into highly distorted MoOx (2 < x < 3) in the WGS reaction. The MoOx on the catalyst surface greatly enhanced the capability of generating active oxygen vacancies to dissociate H2O molecules, which induced unexpectedly superior catalytic performance. Therefore, the intrinsically active surface in the Pt/γ-Mo2N catalyst for the WGS reaction was molybdenum oxide as MoOx (2 < x < 3).

Highly Efficient CuO/α-MnO2 Catalyst for Low-Temperature CO Oxidation.

Copper manganese composite (hopcalite) catalyst has been widely explored for low-temperature CO oxidation reactions. However, the previous reports on the stabilization of such composite catalysts have shown that they deactivated severely under moist conditions. Herein, we developed an α-MnO2 nanorod-supported copper oxide catalyst that is very active and stable for the conditions with or without moisture by the deposition precipitation (DP) method. Incredibly, the CuO/MnO2 DP catalyst (with 5 wt % copper loading) achieves superior activity with a reaction rate of 9.472 µmol-1·gcat-1·s-1 even at ambient temperatures, which is at least double times of that for the reported copper-based catalyst. Additionally, the CuO/MnO2 DP catalyst is significantly more stable than the copper manganese composite catalysts reported in the literature under the presence of 3% water vapor as well as without moisture. A correlation between the catalytic CO oxidation activity and textural characteristics was derived via multitechnique analyses. The results imply that the superior activity of the CuO/MnO2 DP catalyst is associated with the proper adsorption of CO on partially reduced copper oxide as Cu(I)-CO and more surface oxygen species at the interfacial site of the catalyst.

Construction of Active Site in a Sintered Copper-Ceria Nanorod Catalyst.

The construction of stable active site in nanocatalysts is of great importance but is a challenge in heterogeneous catalysis. Unexpectedly, coordination-unsaturated and atomically dispersed copper species were constructed and stabilized in a sintered copper-ceria catalyst through air-calcination at 800 °C. This sintered copper-ceria catalyst showed a very high activity for CO oxidation with a CO consumption rate of 6100 µmolCO·gCu-1·s-1 at 120 °C, which was at least 20 times that of other reported copper catalysts. Additionally, the excellent long-term stability was unbroken under the harsh cycled reaction conditions. Based on a comprehensive structural characterization and mechanistic study, the copper atoms with unsaturated coordination in the form of Cu1O3 were identified to be the sole active site, at which both CO and O2 molecules were activated, thus inducing remarkable CO oxidation activity with a very low copper loading (1 wt %).

Direct Identification of Active Surface Species for the Water-Gas Shift Reaction on a Gold-Ceria Catalyst.

The crucial role of the metal-oxide interface in the catalysts of the water-gas shift (WGS) reaction has been recognized, while the precise illustration of the intrinsic reaction at the interfacial site has scarcely been presented. Here, two kinds of gold-ceria catalysts with totally distinct gold species, <2 nm clusters and 3 to 4 nm particles, were synthesized as catalysts for the WGS reaction. We found that the gold cluster catalyst exhibited a superiority in reactivity compared to gold nanoparticles. With the aid of comprehensive in situ characterization techniques, the bridged -OH groups that formed on the surface oxygen vacancies of the ceria support are directly determined to be the sole active configuration among various surface hydroxyls in the gold-ceria catalysts. The isotopic tracing results further proved that the reaction between bridged surface -OH groups and CO molecules adsorbed on interfacial Au atoms contributes dominantly to the WGS reactivity. Thus, the abundant interfacial sites in gold clusters on the ceria surface induced superior reactivity compared to that of supported gold nanoparticles in catalyzing the WGS reaction. On the basis of direct and solid experimental evidence, we have obtained a very clear image of the surface reaction for the WGS reaction catalyzed by the gold-ceria catalyst.

CeO2@SiO2 Core-Shell Nanostructure-Supported CuO as High-Temperature-Tolerant Catalysts for CO Oxidation.

Supported CuO-CeO2 catalysts have been extensively studied for their outstanding catalytic activity in CO oxidation. Unfortunately, they are prone to sintering and deactivation when exposed to high-temperature automotive exhausts. Herein, taking advantage of the heat-resistant SiO2 microspheres, we fabricated a series of core-shell-structured yCuO- xCeO2@SiO2 ( x is the weight ratio of CeO2-SiO2 and y is the weight ratio of Cu-(CeO2@SiO2)) composite catalysts. All the small CeO2 particles were bound to the SiO2 spheres, forming an xCeO2@SiO2 structure, on the surface of which a certain amount of CuO was well-dispersed. The 5CuO-50CeO2@SiO2 catalyst exhibited good activity, with the full conversion of CO achieved at around 130 °C, and no obvious deactivation was observed in the stability test. Importantly, the interaction between CuO and CeO2@SiO2 enhanced its durability at high temperatures. Even at 800 °C and with a space velocity of 800 000 mL·gcat-1·h-1, CO conversion could be maintained at 90%, which is prospectively applied in a real CO elimination system. The result of the temperature-programmed reduction in hydrogen demonstrated that this special core-shell-structured 5CuO-50CeO2@SiO2 catalyst improved the reduction ability of the CuO species. In situ diffuse reflectance infrared Fourier transform spectroscopy measurements further confirmed that CO molecules preferred to be adsorbed on Cu(I) species to form reactive CO-Cu(I) that enhanced the reactivity of the 5CuO-50CeO2@SiO2 catalyst.