Sm-Mn mixed oxide catalysts prepared by the coprecipitation method were developed, and their catalytic activities were tested for the selective catalytic reduction (SCR) of NO with ammonia at low temperature. The results showed that the amount of Sm markedly influenced the activity of the MnO x catalyst for SCR, that the activity of the Sm-Mn mixed oxide catalyst exhibited a volcano-type tendency with an increase in the Sm content, and that the appropriate mole ratio of Sm to Mn in the catalyst was 0.1. In addition, the presence of Sm in the MnO x catalyst can obviously enhance both water and sulfur dioxide resistances. The effect of Sm on the physiochemical properties of the Sm-MnO x catalyst were investigated by XRD, low-temperature N2 adsorption, XPS, and FE-SEM techniques. The results showed that the presence of Sm in the Sm-MnO x catalyst can restrain the crystallization of MnO x and increase its surface area and the relative content of both Mn4+ and surface oxygen (OS) on the surface of the Sm-MnO x catalyst. NH3-TPD, NO-TPD, and in situ DRIFT techniques were used to investigate the absorption of NH3 and NO on the Sm-MnO x catalyst and their surface reactions. The results revealed that the presence of Sm in the Sm0.1-MnO x catalyst can increase the absorption amount of NH3 and NO on the catalyst and does not vary the SCR reaction mechanism over the MnO x catalyst: that is, the coexistence of Eley–Rideal and Langmuir–Hinshelwood mechanisms (bidentate nitrate is the active intermediate), in which the Eley–Rideal mechanism is predominant.

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Ruthenium (Ru) nanoparticles (∼3 nm) with mass loading ranging from 1.5 to 3.2 wt % are supported on a reducible substrate, cerium dioxide (CeO, the resultant sample is called Ru/CeO), for application in the catalytic combustion of propane. Because of the unique electronic configuration of CeO, a strong metal-support interaction is generated between the Ru nanoparticles and CeO to stabilize Ru nanoparticles for oxidation reactions well. In addition, the CeO host with high oxygen storage capacity can provide an abundance of active oxygen for redox reactions and thus greatly increases the rates of oxidation reactions or even modifies the redox steps. As a result of such advantages, a remarkably high performance in the total oxidation of propane at low temperature is achieved on Ru/CeO. This work exemplifies a promising strategy for developing robust supported catalysts for short-chain volatile organic compound removal.

Tailoring the interfaces between active metal centers and supporting materials is an efficient strategy to obtain a superior catalyst for a certain reaction. Herein, an active interface between Ru and CeO2 was identified and constructed by adjusting the morphology of CeO2 support, such as rods (R), cubes (C), and octahedra (O), to optimize both the activity and the stability of Ru/CeO2 catalyst for propane combustion. We found that the morphology of CeO2 support does not significantly affect the chemical states of Ru species but controls the interaction between the Ru and CeO2, leading to the tuning of oxygen vacancy in the CeO2 surface around the Ru–CeO2 interface. The Ru/CeO2 catalyst possesses more oxygen vacancy when CeO2-R with predominantly exposed CeO2{110} surface facets is used, providing a higher ability to adsorb and activate oxygen and propane. As a result, the Ru/CeO2-R catalyst exhibits higher catalytic activity and stability for propane combustion compared with the Ru/CeO2-C and Ru/CeO2-O catalysts. This work highlights a new strategy for the design of efficient metal/CeO2 catalysts by engineering morphology and associated surface facet of CeO2 support for the elimination of light alkane pollutants and other volatile organic compounds.

Supported gold (Au) nanocatalysts hold great promise for heterogeneous catalysis; however, their practical application is greatly hampered by poor thermodynamic stability. Herein, a general synthetic strategy is reported where discrete metal nanoparticles are made resistant to sintering, preserving their catalytic activities in high-temperature oxidation processes. Taking advantage of the unique coating chemistry of dopamine, sacrificial carbon layers are constructed on the material surface, stabilizing the supported catalyst. Upon annealing at high temperature under an inert atmosphere, the interactions between support and metal nanoparticle are dramatically enhanced, while the sacrificial carbon layers can be subsequently removed through oxidative calcination in air. Owing to the improved metal-support contact and strengthened electronic interactions, the resulting Au nanocatalysts are resistant to sintering and exhibit excellent durability for catalytic combustion of propylene at elevated temperatures. Moreover, the facile synthetic strategy can be extended to the stabilization of other supported catalysts on a broad range of supports, providing a general approach to enhancing the thermal stability and sintering resistance of supported nanocatalysts.

Co3O4 supported on ZSM-5 (Co3O4/ZSM-5) catalysts were prepared by impregnation (IM), deposition precipitation (DP), and hydrothermal (HT) methods. Their catalytic performances for the total oxidation of propane were tested, and their physicochemical properties were investigated by low-temperature N2 adsorption, XRD, FT-IR absorption spectroscopy, XPS, H2-TPR, TEM, and CO chemisorption. The results show that the catalytic activity of Co3O4/ZSM-5 for propane oxidation is higher than that of 1.5 wt % Pd/ZSM-5, and the preparation methods remarkably affect the catalytic activity of Co3O4/ZSM-5. Among four Co3O4/ZSM-5 catalysts prepared by different methods, the catalyst prepared by the HT method possesses the highest catalytic activity for propane oxidation, and their catalytic activities are varied in the order of HT > DP > IM. For the Co3O4/ZSM-5 (DP) catalysts, the precipitant has an evident influence on their catalytic activities. For instance, the DP catalyst prepared with ammonium bicarbonate precipitant has a higher catalytic activity than the catalyst prepared with sodium hydroxide precipitant. The excellent catalytic activity of Co3O4/ZSM-5 (HT) may be attributed to the better reducibility of Co3+, higher Co3+ content, higher surface concentration, and fast migration of the lattice oxygen of Co3O4 on this catalyst. Furthermore, the Co3O4/ZSM-5 catalyst prepared by the HT method exhibits a high stability after being used at 500 °C for 40 h.

Water is perhaps the most common molecule in heterogeneous catalysis, as it is unavoidable in almost any system. Interestingly, it can play completely different roles in the presence of either metals or metal oxides, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] which are the two most common types of the catalysts. On one hand, a moderate amount of water on the surface of late-transition metals such as Au, Pt, and Pd, can promote low-temperature CO oxidation, which is one of the hottest topics in catalysis because of the environmental concerns. [1][2][3][4][5][6] On the other hand, it can be a devastatingly poisonous species on the surface of metal oxides, the best example being the waterinduced deactivation on tricobalt tetraoxide (Co 3 O 4 ). [7][8][9][10][11][12][13][14][15] Specifically, morphology-controlled Co 3 O 4 [7, 16, 17] displays extraordinarily high catalytic activity for CO oxidation at very low temperatures (ca. À77 8C). However, in the presence of trace amounts of water its activity is dramatically reduced. [7][8][9][10][11][12] It is worth emphasizing that transition-metal oxides have received an increasing amount of attention for CO oxidation because of their unexpectedly high catalytic activities, low price, and especially the rich surface chemistry which affords the potential to tune the catalytic properties to a considerable degree. [18][19][20] Moreover, the poisoning effect of H 2 O has also been reported for other oxide-based catalysts such as CuO and MnO x , and it may well be a common issue in many oxide systems. [13][14][15] To comprehend the fundamental role of water in heterogeneous catalysis in general, the following questions need to be answered: What is the mechanism of H 2 O deactivation on Co 3 O 4 oxide? How can one rationalize such a difference between metal and metal oxide systems regarding H 2 O effects? Herein we report a thorough investigation uncovering the origin of the deactivation of Co 3 O 4 by H 2 O and addressing the general effect of H 2 O on metal and metal oxides by using first principles calculations.The deactivation resulting from the presence of water is the main obstacle currently limiting the application of Co 3 O 4 to CO oxidation, and the deactivation mechanism is much debated. The following suggestions regarding the water poisoning effect have been proposed: [7][8][9][10][11][12] 1) water molecules strongly adsorb at the active site, thus blocking the CO adsorption; or 2) water dissociation occurs on the catalyst surface to form a surface OH group that inhibits the adsorption of CO or O 2 ; or 3) the formation of graphitetype carbon deposits or surface carbonate (CO 3 2À ) species. However, no consensus has been reached. To the best of our knowledge, there is only one theoretical study reported concerning the deactivation mechanism at the molecular level, and it focused on the competing effect of the molecular adsorption of H 2 O at active Co 3+ sites. [11b] In this work, almost all the possible deactivation pathways of Co 3 O 4 with regard to wa...

Pd/H-ZSM-5 catalysts could completely catalyze CH 4 to CO 2 at as low as 320 °C, while there is no detectable catalytic activity for pure H-ZSM-5 at 320 °C and only a conversion of 40% could be obtained at 500 °C over pure H-ZSM-5. Both the theoretical and experimental results prove that surface acidic sites could facilitate the formation of active metal species as the anchoring sites, which could further modify the electronic and coordination structure of metal species. PdO x interacting with the surface Bronsted acid sites of H-ZSM-5 could exhibit Lewis acidity and lower oxidation states, as proven by the XPS, XPS valence band, CO-DRIFTS, pyridine FT-IR, and NH 3 -TPD data. Density functional theory calculations suggest PdO x groups to be the active sites for methane combustion, in the form of [AlO 2 ]Pd(OH)-ZSM-5. The stronger Lewis acidity of coordinatively unsaturated Pd and the stronger basicity of oxygen from anchored PdO x species are two key characteristics of the active sites ([AlO 2 ]Pd(OH)-ZSM-5) for methane combustion. As a result, the PdO x species anchored by Brønsted acid sites of H-ZSM-5 exhibit high performance for catalytic combustion of CH 4 over Pd/H-ZSM-5 catalysts.