Temperature-programmed Reaction Experiments Research Articles

Impact of mild hydrothermal aging on kinetics of NH[formula omitted], NO, SO[formula omitted] and CO oxidation reactions on Cu/SSZ-13 catalyst

Cu/SSZ-13 is a catalyst commonly used for selective catalytic reduction (SCR) of nitrogen oxides (NOx) in diesel engine exhaust. Standard configurations are based on SCR preceded by an oxidation catalyst, however, a close-coupled SCR configuration appears relevant for upcoming regulations addressing cold-start emissions. Two often discussed ion-exchanged Cu sites in Cu/SSZ-13 are denoted ZCuOH and Z2Cu, where Z represents an Al atom in the zeolite framework. Mild hydrothermal aging (HTA) causes Cu redistribution within the catalyst; ZCuOH sites transform into more stable Z2Cu species. In this work, the effect of mild HTA on NH3, NO, SO2, and CO oxidation is studied on a commercial Cu/SSZ-13 sample. Temperature-programmed reaction experiments, performed in a lab reactor, and previously published catalyst characterization data using H2-TPR, NH3-TPD, and DRIFTS were used to build and validate a mathematical model. It couples the kinetics of the oxidation reactions with ZCuOH and Z2Cu concentration evolution during mild HTA. The model uses two distinct rate coefficients for ZCuOH and Z2Cu sites, allowing prediction of the catalyst activity during aging. The results suggest that the rate coefficients for the studied reactions on Z2Cu are effectively nil, so the observed activity in NH3, NO, SO2, and CO oxidation can be attributed solely to ZCuOH sites.

Ni-BaMnO3 Perovskite Catalysts for NOx-Assisted Soot Oxidation: Analyzing the Effect of the Nickel Addition Method

In this study, we analyzed the role of a series of BaMn1−xNixO3 (x = 0, 0.2, and 0.4) mixed oxide catalysts, synthesized using the sol–gel method, in NOx-assisted diesel soot oxidation. ICP-OES, XRD, XPS, and H2-TPR techniques were used for characterization and Temperature-Programmed Reaction experiments (NOx-TPR and Soot-NOx-TPR), and isothermal reactions at 450 °C (for the most active sample) were carried out to determine the catalytic activity. All samples catalyzed NO and soot oxidation at temperatures below 400 °C, presenting nickel-containing catalysts with the highest soot conversion and selectivity to CO2. However, the nickel content did not significantly modify the catalytic performance, and in order to improve it, two catalysts (5 wt % in Ni) were synthesized via the hydrothermal method (BMN2H) and the impregnation of nickel on a BaMnO3 perovskite as support (M5). The two samples presented higher activity for NO and soot oxidation than BMN2E (obtained via the sol–gel method) as they presented more nickel on the surface (as determined via XPS). BMN2H was more active than M5 as it presented (i) more surface oxygen vacancies, which are active sites for oxidation reactions; (ii) improved redox properties; and (iii) a lower average crystal size for nickel (as NiO). As a consequence of these properties, BMN2H featured a high soot oxidation rate at 450 °C, which hindered the accumulation of soot during the reaction and, thus, the deactivation of the catalyst.

Tailoring the Composition of BaxBO3 (B = Fe, Mn) Mixed Oxides as CO or Soot Oxidation Catalysts in Simulated GDI Engine Exhaust Conditions.

Mixed oxides with perovskite-type structure (ABO3) are promising catalysts for atmospheric pollution control due to their interesting and tunable physicochemical properties. In this work, two series of BaxMnO3 and BaxFeO3 (x = 1 and 0.7) catalysts were synthesized using the sol-gel method adapted to aqueous medium. The samples were characterized by μ-XRF, XRD, FT-IR, XPS, H2-TPR, and O2-TPD. The catalytic activity for CO and GDI soot oxidation was determined by temperature-programmed reaction experiments (CO-TPR and soot-TPR, respectively). The results reveal that a decrease in the Ba content improved the catalytic performance of both catalysts, as B0.7M-E is more active than BM-E for CO oxidation, and B0.7F-E presents higher activity than BF for soot conversion in simulated GDI engine exhaust conditions. Manganese-based perovskites (BM-E and B0.7M-E) achieve better catalytic performance than iron-based perovskite (BF) for CO oxidation reaction due to the higher generation of actives sites.

BaFe1−xNixO3 Catalysts for NOx-Assisted Diesel Soot Oxidation

AbstractIn this work, it is analyzed the effect of the partial substitution of Fe by Ni in a BaFeO3 perovskite to be used as the catalyst for NOx-assisted diesel soot oxidation. A series of BaFe1−xNixO3 (x = 0, 0.2, 0.4 and 0.8) catalysts have been synthesized by using the sol–gel method. The catalysts have been characterized by ICP-OES, XRD, XPS, O2-TPD, H2-TPR- and TEM. The catalytic activity for NO to NO2 oxidation and NOx-assisted diesel soot oxidation have been determined by Temperature Programmed Reaction experiments (NOx -TPR and Soot-NOx-TPR, respectively) and by isothermal reaction at 450 °C. Ni seems not to be inserted in the BaFeO3 perovskite and, instead of that, BaNiO3 perovskite and NiO are detected on the surface of the perovskite BaFeO3. XPS data reveal the coexistence of Fe(III) and Fe(IV) on the catalyst’s surface (being Fe(III) the main oxidation state) and the presence of oxygen vacancies. All catalysts are active for NO oxidation to NO2, showing BaFeO3 and BaFe0.6Ni0.4O3 the best catalytic performance. BaFe0.6Ni0.4O3 shows the highest proportion of nickel on surface and it combines the highest activity and stability for NOx-assisted diesel soot oxidation. Also, this catalyst presents the highest initial soot oxidation rate which minimizes the accumulation of unreacted soot during reaction.

To the question of oxidation on the surface of oxides: temperature- programmed oxidation of cyclohexanol

Temperature-programmed reaction (TPR) method with mass spectrometric control of the products was used to study of cyclohexanol oxidation into cyclohexanone on individual and mixed oxides supported by γ-Al2O3 and silica gel. In the TPR profiles the temperature of a maximum rate of cyclohexanone formation varies from 125°C for MoO3/Al2O3 to 235°C for less active CuO/Al2O3. The catalytic activity of individual oxides decreases in the order MoO3/Al2O3> V2O5/SiO2 > Fe2O3/Al2O3 > Bi2O5/Al2O3 > TiO2/SiO2 ≈ СeO2/Al2O3 > TiO2/Al2O3 > SnO2/Al2O3. As "reactive" oxygen in our TPR experiment was supplied only from oxide lattice, oxide activity is determined by different energy of the surface Me – O bonds. The approach to search for mixed active oxides based on decreasing coordination number of O2- ions is proposed, that confirmed by the example of CuO-WO3/Al2O3 catalyst. The mixed supported oxides, especially CuOCrO3/Al2O3, CuO-MoO3/Al2O3, MoO3-SnO2/Al2O3 and Bi2O3–SnO2/Al2O3, are more active in С6Н12О + 1/2О2 → С6Н10О + Н2О oxidation. The synthesized CuO-CrO3/Al2O3 catalyst provides cyclohexanone formation without side cyclohexanol dehydration and can be used for the oxidation of ethylene glycol – methanol mixture into methyl glycolate. CuO-Cr2O3/Al2O3 with a spinel structure of CuCr2O4 ([CuO4] 6− tetrahedra, Cu2+ sp3-hybridization) is more active in cyclohexanol oxidation than CuO/Al2O3 with flat [CuO4] 6−squares, Cu2+ dsp2-hybridization. This is explained by the lower energy of Cu-O bonds at sp3-hybridization of Cu2+ ions.

Sorption and Reaction of Biomass Derived HC Blends and Their Constituents on a Commercial Pt–Pd/Al2O3 Oxidation Catalyst

Within the Research Cluster of Excellence “The Fuel Science Center” at RWTH Aachen University, the production and application of new fuels from bio-based carbon feedstocks and CO2 with hydrogen from renewable electricity generation is being investigated. In this study, the storage and oxidation of ethanol, 1-butanol, 2-butanone, cyclopentanone, and cyclopentane as well as two blends thereof on a series production Pt–Pd/Al2O3 oxidation catalyst were investigated. Hydrocarbon (HC) storage and temperature-programmed surface reaction (TPSR) experiments were carried out to analyze their adsorption and desorption behavior. In addition, the individual HCs and both blends were investigated using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (TP-DRIFTS). In general, all oxygenated HCs are adsorbed more strongly than cyclopentane due to their higher polarity. Interestingly, it could be observed that the two different blends [blend 1: ethanol (50 mol %), 2-butanone (21 mol %), cyclopentanone (14 mol %) and cyclopentane (15 mol %); blend 2: 1-butanol (45 mol %), ethanol (29 mol %) and cyclopentane (27 mol %)] exhibit a different storage behavior compared to the single hydrocarbons. It was shown that the presence of 1-butanol and cyclopentane in blend 2 strongly inhibits the oxidation of ethanol. As a result, the ethanol light-off temperature was increased by at least 100 K. A difference was also found in the storage behavior of cyclopentane. While no significant storage could be detected in the pure compound experiment, the experiments with both mixtures showed a larger amount stored. The presence of adsorbed species of the hydrocarbons and their corresponding reaction products has been demonstrated and gives an insight into the storage mechanism of blends.Graphic

Electrochemical activation of Ru catalyst with alkaline ion conductors for the catalytic decomposition of ammonia

• Ammonia decomposition on Ru catalyst is electrochemically activated with Na and K. • The promotion effect is higher with K than Na. • The promotion is due to a strengthening of the bond of weakly adsorbed N species. • Under optimal conditions the hydrogen production rate increased above 230% • The EPOC effect allows catalyst activation at low temperatures. This study reports the electrochemical activation (EPOC) of ruthenium catalyst film with alkaline ion conductors for hydrogen production via catalytic decomposition of ammonia. Two electrocatalysts, Ru/Na-βAl 2 O 3 and Ru/K-βAl 2 O 3 have been prepared, characterized, and tested under low temperature reaction conditions (250–350 °C). The electrochemically supply of moderate amounts of alkaline ions (Na + and K + ) from the solid electrolyte support to the ruthenium catalyst film, activated the hydrogen production rate. The promotional effect has been attributed to a strengthening of the chemisorptive bond of weakly adsorbed N surface species, which stabilizes N adsorbed molecules on the ruthenium catalyst surface and thus facilitating the ammonia decomposition reaction. Among the two alkali ions, the effect of potassium was stronger, increasing the hydrogen production rate above 230% at 300 °C under optimally conditions. Temperature programmed reaction experiments also confirms the interest of EPOC for the activation of the catalyst at low temperatures.

In Situ Observation of the Formation of Fe-N4 Sites Via Metalation during the Pyrolysis of Fe Precursors and N-Doped Carbon Matrix

A clear understanding of the formation mechanism of single atom M-N4 sites (M represents transition metals such as Mn, Fe, Co, etc) is required for rational synthesis of M-N-C catalysts for the oxygen reduction reaction (ORR) in fuel cells. Herein, multi-component characterizations including in-temperature x-ray absorption spectroscopy and temperature-programmed reaction experiments were combined to unravel the formation of Fe-N4 sites during pyrolysis. Two synthesis routes were used to form Fe-N4 sites: (1) pyrolyzing the mixture of FeCl2·4H2O with zeolitic imidazolate framework (ZIF8)-derived N-doped carbon matrix (N-C); (2) implementing the chemical vapor deposition (CVD) of FeCl3 vapor onto the N-C at 750 ℃ wherein the FeCl3 and N-C are separately placed without direct physical contact.We found in the synthesis route (1) the FeCl2·4H2O transforms to metal oxides, followed by the formation of single-atom tetrahedral Fe-O4 sites as the temperature increases to 600 ℃.1 The Fe-O4 then gradually transforms to Fe-N4 as the temperature gradually increases from 600 ℃ to 1000 ℃. We accordingly propose that the Fe-O4 reacts with the Zn-N4 in the N-C forming Fe-N4 via metalation: Fe-O4 + Zn-N4 ↔ Fe-N4 + Zn-O4, followed by the carbothermic reaction: ZnO + C ↔ Zn (vapor) + CO around 950 ℃. This is different from our previous hypothesis that the Fe-O4 releases a single Fe atom that is captured by a N4-C cavity forming Fe-N4.1 Higher temperature promotes the metalation due probably to the comparative thermostability between Fe-O4 and Fe-N4, plus driving the formation of Zn vapor that leaves the N-C. In addition, if the Fe-O4 is not in proximity with the Zn-N4 during pyrolysis, the Fe-O4 transforms to small nanoparticles or FeOx rather than Fe-N4. Therefore, high pyrolysis temperature and sufficient mix of the Fe precursor and N-C are two salient features of this synthesis route that is essentially the same as the traditional synthesis route. These two features severely limit the Fe-N4 site density in the synthesized Fe-N-C, because Fe-N4 decomposes at elevated potentials and Fe-N4 sites are formed throughout the N-C and only those on surface accessible by air are ORR-active. These limitations are alleviated in the CVD route wherein the Fe-N4 is formed via a different metalation process: FeCl3 (vapor) + Zn-N4 ↔ Fe-N4 + ZnCl2 (vapor). The boiling point of ZnCl2 (732 ℃) is more than 200 ℃ lower than that of Zn (950 ℃), which leads to an optimistic pyrolysis temperature of 750 ℃ rather than 1000±100 ℃ in traditional synthesis. In addition, Fe-N4 sites are formed exclusively on the surface sites of the N-C accessible by FeCl3 vapor, and they are thus accessible by air. Consequently, we demonstrated a highly active Fe-N-C ORR catalyst synthesized via CVD at 750 ℃ with a surface Fe-N4 site density of 1.8 wtFe% with full site utilization of Fe-N4 sites. We also showed that the CVD synthesis route is applicable for the synthesis of M-N-C with other elements such as Mn and Co. Acknowledgements This work was supported by the US Department of Energy under award number DE-EE0008416 and DE-EE0008075. The authors acknowledge the support from the DOE Energy Efficiency and Renewable Energy Fuel Cell Technologies Office (DOE-EERE-FCTO) ElectroCat consortium. This research used beamline 6-BM and 8-ID (ISS) of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704. Argonne is a U.S. Department of Energy Office of Science Laboratory operated under Contract No. DE-AC02-06CH11357 by UChicago Argonne, LLC.(1) Li, J.; Jiao, L.; Wegener, E.; Richard, L. L.; Liu, E.; Zitolo, A.; Sougrati, M. T.; Mukerjee, S.; Zhao, Z.; Huang, Y.; Yang, F.; Zhong, S.; Xu, H.; Kropf, A. J.; Jaouen, F.; Myers, D. J.; Jia, Q. J. Am. Chem. Soc. 2020, 142, 1417-1423.

Mechanistic insights into the conversion of dimethyl ether over ZSM-5 catalysts: A combined temperature-programmed surface reaction and microkinetic modelling study

The rates of adsorption, desorption, and surface reaction of dimethyl ether (DME) to olefins over fresh and working ZSM-5 catalysts with different Si/Al ratios (36 and 135) were decoupled using a combination of temperature-programmed surface reaction experiments and microkinetic modelling. Transient reactor performance was simulated by solving coupled 1D nonlinear partial differential equations accounting for elementary steps during the induction period based on the methoxymethyl mechanism on the zeolite catalyst and axial dispersion and convection in the reactor. Propylene is the major olefin formed, and site-specific scaling relations between the activation energies of DME desorption and barriers to the formation of methoxymethyl and methyl propenyl ether are observed. Six ensembles of sites are observed with a maximum of three adsorption/desorption sites and three adsorption/desorption/reaction sites. Barriers are generally higher for working catalysts than fresh catalysts. Activation energies of propylene formation of ca. 200 kJ mol−1 are obtained, corroborating direct mechanistic proposals.

A Simple Angle-Resolved Thermal Molecular Beam Reactor: Applied to CO Oxidation on Pt{110}

We developed a simple form of thermal molecular beam catalytic reactor system which is capable of measuring sticking probabilities and reaction probabilities, together with angle-resolved scattering of molecules and products during catalytic reactions at the surface. This includes very fast determination of the angle dependence of the reaction product flux at steady-state. It was employed to determine the oxidation of CO on Pt{110}-(1 × 2), including individual molecular sticking and scattering. The initial sticking probability of oxygen on Pt{110} shows a small variation between 140 and 750 K surface temperature, from 0.45 to 0.28. The saturation uptake drops from 1.5 ± 0.2 ML at 140 K to 0.6 ML at 300 K and to 0.23 ± 0.02 ML at 750 K. The initial sticking probability of CO at 300 K is 0.80 and decreases to 0.62 at 470 K. Beyond that temperature, it descends steeply down to near zero at 570 K, due to the high desorption rate of CO at that temperature. Kisliuk precursor mobility parameters K were calculated from shape of the sticking curves. For 300 K, a value of 0.11 ± 0.01 was found, which increases to 0.76 ± 0.01 at 470 K, indicating a change from considerable mobility in the precursor state, to more limited mobility before desorption at high temperature. In temperature-programmed CO-O2 reaction experiments, CO2 production was observed to initiate in the temperature region 460–510 K. Using isothermal angle-resolved experiments, the CO2 flux was determined in the [11¯0] plane at temperatures of 470–620 K. Two sharp scattering lobes at positions of ±16° off the surface normal were found, with a high cosine power angle dependence, which were attributed to desorption from the {111}-like microfacets of the 1 × 2 reconstructed surface, with products evolving over a high barrier.

Ethanol Conversion over La0.7Sr0.3MnO3–x(100): Autocatalysis, Adjacent O-Vacancies, Disproportionation, and Dehydrogenation

The mechanism for catalytic conversion of ethanol over La0.7Sr0.3MnO3–x(100) surface to acetaldehyde and ethene was investigated. Pre-exposure temperature-programmed reaction (PE-TPR) experiments w...

Surface Reactions and Catalytic Activities for Small Alcohols over LaMnO3(100) and La0.7Sr0.3MnO3(100): Dehydrogenation, Dehydration, and Oxidation

The surface chemistry and catalytic activity of small alcohols (methanol, ethanol, and propan-2-ol) were studied over LaMnO3(100) and La0.7Sr0.3MnO3(100) thin films. The observed C-containing products corresponded to products typically associated with dehydrogenation (methanal, ethanal, and propanone), dehydration (ethene and propene), and oxidation (COx). No coupling products were observed. Two types of temperature-programmed reaction experiments (TPR) were performed: pre-exposure TPR (PE-TPR) experiments in which the reactant is preadsorbed and the temperature is then ramped, as well as continuous exposure TPR (CE-TPR) experiments during which the reactants are continuously introduced and the temperature is ramped. Mechanistic pathways are proposed based on the results and literature, including removal of lattice oxygens by surface hydrogens, organic intermediates adsorbed in oxygen vacancies, C–H bond breaking by alkoxy disproportionation reactions, and direct C–H bond breaking. The vacancy related pat...

Sn-modification of Pt7/alumina model catalysts: Suppression of carbon deposition and enhanced thermal stability.

An atomic layer deposition process is used to modify size-selected Pt7/alumina model catalysts by Sn addition, both before and after Pt7 cluster deposition. Surface science methods are used to probe the effects of Sn-modification on the electronic properties, reactivity, and morphology of the clusters. Sn addition, either before or after cluster deposition, is found to strongly affect the binding properties of a model alkene, ethylene, changing the number and type of binding sites, and suppressing decomposition leading to carbon deposition and poisoning of the catalyst. Density functional theory on a model system, Pt4Sn3/alumina, shows that the Sn and Pt atoms are mixed, forming alloy clusters with substantial electron transfer from Sn to Pt. The presence of Sn also makes all the thermally accessible structures closed shell, such that ethylene binds only by π-bonding to a single Pt atom. The Sn-modified catalysts are quite stable in repeated ethylene temperature programmed reaction experiments, suggesting that the presence of Sn also reduces the tendency of the sub-nano-clusters to undergo thermal sintering.

Controlling Hydrogenation Selectivity by Size: 3-Hexyne on Supported Pt Clusters

Size-selected metal clusters supported on metal oxides have recently gained significant scientific attention because of their potential to investigate hydrogenation reactions on a fundamental level. To expand previous studies on ethylene hydrogenation, we report the selective hydrogenation of 3-hexyne using the same model systems of Pt clusters supported on MgO, but introducing the additional parameter of reaction selectivity. Isotopically labeled temperature-programmed reaction experiments show that the surface chemistry of 3-hexyne is dependent on cluster size and characterized by desorption of several reaction products. The latter include formation of molecules involving dehydrogenation as well as hydrogenation steps. By comparison between hydrogenation of hexyne and ethylene, an atomic window is found for Pt9, where activation barriers favor triple- over double-bond hydrogenation, effectively leading to enhanced selectivity. The favored hydrogenation of the triple bond is caused by cluster morphology ...

Effect of Sr Substitution in LaMnO3(100) on Catalytic Conversion of Acetic Acid to Ketene and Combustion-Like Products

The chemistry of acetic acid reactions was studied over La1–xSrxMnO3(100) surfaces (x = 0, 0.3, or 0.7). Two types of temperature-programmed reaction (TPR) experiments were performed: pre-exposure ...

A highly active and stable bimetallic Ni-Mo2C catalyst for a partial oxidation of jet fuel

Mo2C is an attractive catalyst for fuel reforming reactions because it possesses both a high activity and a high coking resistance. However, Mo2C catalysts cannot guarantee sufficient long-term stability during fuel reforming reactions that operate at a high fuel flow rate due to their phase instability. The present investigation is focused on improving the phase stability and the performance of Mo2C by addition of Ni for the partial oxidation (POX) of jet fuel. Mo2C and Ni-Mo2C were first prepared from CH4/H2 carburization of synthesized MoO3 and NiMoO4, respectively. To investigate the catalytic activity of carburized catalysts for the POX of jet fuel, tests were conducted at 750 °C and 1 atm, with a weight-hourly-space-velocity (WHSV) of 42 h−1 and O2/C ratio of 0.6. The Mo2C sample without Ni shows a performance similar to that of a blank run (in the absence of catalyst) with 70% conversion, 12% H2 yield, and 53% CO yield. The poor performance of Mo2C is due to its partial phase transformation into the MoO2 phase at the high WHSV. For Ni-Mo2C, the catalyst exhibits excellent stability over the 24 h test period with carbon conversion of 90% and H2 and CO yields of 56 and 63%, respectively. There were no indications of bulk oxidation or surface coking. Temperature-programmed reaction and isotopic exchange experiments showed that Ni-Mo2C follows the “catalytic oxidation and re-carburization cycle.” In this cycle, molecular oxygen is activated over the Mo2C surface, and the activated oxygen species react with lattice carbons from Mo2C to produce both CO and carbon vacancies. Hydrocarbons are decomposed into H2 and surface carbons over the metallic Ni sites. To sustain the catalytic cycle, the Mo2C1-x phase (i.e., non-stoichiometric Mo2C with carbon vacancies) is re-carburized by the surface carbons deposited on the metallic Ni sites. Finally, our results also showed that NiMoO4 can be rapidly carburized in-situ to form a high performance Ni-Mo2C catalyst under a flowing mixture of n-dodecane and air.

Crystal-Plane-Dependent Fischer–Tropsch Performance of Cobalt Catalysts

Identification of the crystal plane effect of the Co derived from Co3O4 nanocrystals (NCs) on Fischer–Tropsch synthesis (FTS) is important for developing high-performance FTS solid catalysts. However, the achievement of this goal is hindered by the complexity of the FTS and the absence of sufficient crystallographic structure data. In this study, we report that the experimental FT performance of the Co catalysts depends on the exposed crystal facets of the Co3O4 NCs. The exposed Co3O4 NC {112} facets have the highest catalytic activity and the lowest methane selectivity (6.2%) in comparison to those of the {111} and {001} planes. The evolution of the crystal planes during the reduction was investigated further, and the preferred orientation relationship induced by the Co3O4 → Co transformation was {112} → {10–11}, {111} → {0001}, and {001} → {11–20}. CO temperature-programmed surface reaction experiments and density functional theory calculations further verified that the high FT performance of Co3O4{112}...

Temperature-programmed plasma surface reaction: An approach to determine plasma-catalytic performance

Plasma-enhanced heterogeneous catalysis offers a promising alternative to thermal catalysis due to the synergy between the plasma and the solid catalyst. However, there is only a limited mechanistic insight about the interactions of highly energetic electrons and excited molecules with heterogeneous catalysts in plasmas. Accurate performance comparison in a plasma-catalytic setting is complicated because of the intricate nature of the plasma-catalyst system: simultaneous reactions occurring in the gas-phase and at the catalytic surface; the dependence of the discharge on dielectric properties of the packed catalyst bed; and the dependence of permittivity and polarization of the catalyst on plasma parameters. Here, we present a method of temperature-programmed plasma surface reaction (TPPSR) that allows decoupling gas-phase processes from the surface plasma-induced reactions. Using this method we reveal the main reasons of apparent synergy between plasma and heterogeneous catalyst for the case of carbon dioxide hydrogenation. Experiments with isotopically labelled CO2 and temperature-programmed plasma reaction experiments in flow of CO2/H2 prove a substantial role of gas-phase dissociation/hydrogenation for the observed catalyst activity and selectivity. The product distribution and reaction pathways do not significantly depend on the discharge parameters. Taking into account overheating of the catalytic bed for comparison of catalytic activity with and without plasma, it was concluded that energy dissipation also plays an important role. The observed plasma enhancement is in part due to the acceleration of electron-induced surface reactions.

Catalytic oxidation of nitrogen containing compounds for nitrogen determination

The high temperature catalytic oxidation (HTCO) performance of Al2O3 supported Pt, Cu, Cu-Ce and Fe catalysts were systematically studied with a perspective of selective oxidation of nitrogenous compounds to nitric oxide for quantitative determination of bound nitrogen. The catalyst samples were prepared via impregnation and characterized by XRD and BET. In addition, temperature programmed reaction experiments with acetonitrile and oxygen were conducted to evaluate the catalytic activity and selectivity toward N2, N2O and NO. The catalyst samples were also tested for model components; urea, EDTA, pyridine, glutamic acid and ammonium sulfate representing different functional groups.The conversion of acetonitrile was tended to increase in the order of Cu-Ce/Al2O3>Cu/Al2O3>Pt/Al2O3>Fe/Al2O3 at around 500 °C and almost complete conversion of acetonitrile was achieved at 700 °C over the all catalyst samples studied. Temperature programmed reaction experiments indicated that two reaction routes, direct oxidation of cyanide species and oxidation of ammonia formed by hydrolysis of cyanide species determine NO selectivity. Direct oxidation of cyanide species is favored over Pt/Al2O3 catalyst which exhibit highest NO yield (93%) at 700 °C. The second route, hydrolysis of cyanide species to ammonia which is further oxidized to N2, NO and NO2 was evidenced by TPR-FTIR analyses over Fe/Al2O3, Cu/Al2O3 and Cu-Ce/Al2O3 catalysts. Among these catalysts, highest NO yield (90%) was observed over Fe/Al2O3 at 700 °C which is comparable to Pt/Al2O3 catalyst. For Cu and Cu-Ce/Al2O3 catalyst, lower yields were obtained due to higher N2 selectivity. Similar results were obtained from benchmark tests performed by model nitrogen components representing different functional groups. Pt/Al2O3 and Fe/Al2O3 catalysts possessed higher oxidation activities and nitrogen recoveries than Cu and Cu-Ce catalysts. As a result, Fe/Al2O3 catalyst is highly effective, lower cost alternative to existing Pt based catalysts which are used for bound nitrogen determination.

Steady-State Catalytic Decomposition of Aspartic Acid on Cu(111)

Decomposition of tartaric acid (TA, HO2CCH(OH)CH(OH)CO2H) and aspartic acid (Asp, HO2CCH(NH2)CH2CO2H) on Cu surfaces occurs via a vacancy-mediated surface explosion mechanism with nonlinear kinetics: re = keθ(1 – θ)2, where θ is the adsorbate coverage, and (1 – θ) is the vacancy coverage. During temperature-programmed reaction experiments on naturally chiral Cu(hkl)R&S surfaces, these kinetics, coupled with the chirality of the adsorbates, lead to highly enantiospecific decomposition rates. Herein, it is demonstrated that, in the presence of a thermal molecular beam with a constant Asp flux, FAsp, the decomposition of Asp on Cu(111) occurs catalytically and in steady-state to turnover numbers >40 without contamination or deactivation of the surface. Moreover, the decomposition rates at a given (T, FAsp) manifest the two different steady-states predicted by the nonlinearity of the decomposition kinetics. The unusual ability to catalytically decompose Asp on Cu, coupled with the ability to distinguish between d- and 13C-l-Asp using mass spectrometry, opens an avenue for the future study of enantioselective catalysis on Cu(hkl)R&S surfaces.