Reduced Copper Species Research Articles

Catalytic performance of commercial Cu-ZSM-5 zeolite modified by desilication in NH3-SCR and NH3-SCO processes

In the presented manuscript an influence of the mesoporosity generation in commercial ZSM-5 zeolite on its catalytic performance in two environmental processes, such as NO reduction with ammonia (NH3-SCR, Selective Catalytic Reduction of NO with NH3) and NH3 oxidation (NH3-SCO, Selective Catalytic Oxidation of NH3) was examined. Micro-mesoporous catalysts with the properties of ZSM-5 zeolite were obtained by desilication with NaOH and NaOH/TPAOH (tetrapropylammonium hydroxide) mixture with different ratios (TPA+/OH- = 0.2, 0.4, 0.6, 0.8 and ∞) and for different durations (1, 2, 4 and 6 h). The results of the catalytic studies (over the Cu-exchanged samples) showed higher activity of this novel mesostructured group of zeolitic materials. Enhanced catalytic performance was related to the generated mesoporosity (improved Hierarchy Factor (HF) of the samples), that was observed especially with the use of Pore Directing Agent (PDA) additive, TPAOH. Applied desilication conditions did not influence significantly the crystallinity of the samples (X-ray diffraction analysis (XRD)), despite the treatment for 6 h in NaOH solution, which was found to be too severe to preserve the zeolitic properties of the samples. The modified porous structure and accessibility of acid sites (increased surface acidity determined by temperature programmed desorption of ammonia (NH3-TPD)) influenced the red-ox properties of copper species introduced by ion-exchange method (temperature programmed reduction with hydrogen (H2-TPR). Increased acidity of the micro-mesoporous samples, as well as the content of easily reducible copper species resulted in a significant improvement of Cu-ZSM-5 catalytic efficiency in the NH3-SCR and NH3-SCO processes.

Rapid synthesis of Fe-doped CuO-Ce0.8Zr0.2O2 catalysts for CO preferential oxidation in H2-rich streams: Effect of iron source and the ratio of Fe/Cu

Abstract A facile route (urea grind combustion method) is described for the rapid synthesis of Fe-doped Cu-Ce-Zr catalysts within 30 min through simple grinding and combustion. The effects of iron source and Fe/Cu mass ratio on the performances of the catalysts for CO preferential oxidation (CO-PROX) are evaluated. The influences of H 2 O, CO 2 , and their mixture on the activity as well as stability of the catalysts are also investigated. The samples are characterized by XRD, N 2 adsorption-desorption, H 2 -TPR, TEM, Raman and XPS. Fe(NO 3 ) 3 is found to be superior to FeCl 3 and Fe 2 (SO 4 ) 3 as the iron source for Fe-CuCZ catalyst. Among the different synthesized catalysts, 1/10Fe (N) -CuCZ is found to be the most active catalyst, indicating that the optimal Fe/Cu mass ratio is 1/10. The influences of H 2 O, CO 2 , and H 2 O + CO 2 on the catalytic performance of 1/10Fe (N) -CuCZ are in the order of CO 2 2 + H 2 O 2 O. 1/10Fe (N) -CuCZ exhibits excellent stability during a 228 h time-on-stream test. 1/10Fe (N) -CuCZ shows the highest catalytic activity and excellent stability even in the presence of H 2 O and CO 2. The excellent catalytic performance can be attributed to the synergy between the highly dispersed copper species and ceria, as well as the formation of more oxygen vacancies and reduced copper species.

Spontaneous Reduction of Cupric Complex on Titanium Oxides in Acidic Sulfate–Chloride Media

It is discovered in this work that Cu(II) can be spontaneously reduced on titanium oxides in a mixed sulfate-chloride solution at 85°C. X-ray photoelectron spectroscopy (XPS) suggests that after reaction, copper species exist in an oxidation state lower than 2+. Analysis using X-ray powder diffraction (XRD) shows that the reduced copper species could exist in the form of a CuTi alloy. Time of flight secondary ion mass spectrometry (ToF-SIMS) revealed the depth profile of copper signals in the oxide films. ToF-SIMS results demonstrated that copper signals co-existed with titanium oxide signals in the anodized oxide films, and copper species can diffuse deeply into the porous films within 60 minutes of immersion. Further electrochemical and surface characterizations have confirmed that the presence of chloride ions is a crucial factor for the spontaneous reduction of Cu(II). This phenomenon reveals the role of Cu(II) in a mixed sulfate-chloride solution and its effect on titanium oxide films. It also provides an approach to incorporate a CuTi alloy into titanium oxide films.

Electrochemical Stability of Cu–10Al–10Zn, Cu–10Al–10Ni, and Cu–10Ni–10Zn Ternary Alloys in Simulated Physiological Solutions

Copper-based alloys are widely used in the consumer electronics industry for components such as connector contacts, shielding gaskets, and terminals. Nickel silver is a general term for alloys that contain copper, nickel, and zinc. Nickel silver first became popular as a base metal for silver-plated cutlery and other silverware, notably electro-plated nickel silver, jewelery and coins. In this article, the electrochemical stability of Cu–10Ni–10Zn alloy was compared with that of pure copper and two of copper ternary alloys, namely Cu–10Al–10Zn and Cu–10Al–10Ni in synthetic sweat solution, Hank’s solution and in Ringer physiological solution. Corrosion behavior of the different electrodes was investigated using cyclic voltammetry, potentiodynamic polarization, and impedance spectroscopy techniques. The CVs showed peaks concerning the redox reactions for copper. These peaks were assigned to the formation and reduction of copper species. Furthermore, they showed that the copper oxidation was suppressed to a large extent by the presence of Ni and zinc in the alloy composition than the presence of Al and Zn or the presence of Al and Ni elements. Also, the results showed that the Cu–10Ni–10Zn alloy exhibited good corrosion resistance due to the formation of a protective passive film. The electrochemical impedance spectroscopy results indicated that either a duplex film with an inner barrier layer and an outer porous layer or a single passive layer was formed on the surface. The formation of such passive film was discussed, and the different alloy surfaces examined by scanning electron microscopy and subjected to EDAX analysis. The surface analysis has shown the participation of the different alloying elements in the passive film according to the alloy constituents. Addition of Ni decreases the rate of corrosion of the Cu, and the Cu–10Ni–10Zn was found to be the most corrosion-resistant alloy.

Improved photocatalytic activity of nano CuO-incorporated TiO2 granules prepared by spray drying

4wt% CuO–96wt% TiO2 granules were prepared by a spray drying process. The microstructure and optical property of CuO–TiO2 granules were studied. The results indicate that copper existed in the form of CuO. The spray dried granules possess spherical geometry and smooth surface with grain size in the range of 40–80μm. CuO–TiO2 has a relatively smaller Eg value (2.85eV) than TiO2 (3.17eV). The photocatalytic property of CuO–TiO2 granules was investigated by degradation of a model pollutant (the azo dye methyl orange) under the irradiation of the xenon lamp equipped with a band pass filter of 365nm. The CuO–TiO2 spray-dried granules degrade about 10% more MO than TiO2 spray-dried granules under UV irradiation within the same time. The XPS spectra suggested that Cu2+ and reduced copper species were coexistent in reacted CuO–TiO2 photocatalyst. The improvement of photocatalytic activity for CuO–TiO2 was mainly attributed to effective separation of photo-generated electron–hole pairs in the presence of CuO.

Near-ambient XPS characterization of interfacial copper species in ceria-supported copper catalysts.

Catalysts based on combinations of copper and cerium oxides are interesting alternatives to noble metal ones for processes involved in the production/purification of hydrogen produced from hydrocarbons or biomass like the water-gas shift or the preferential oxidation of CO reactions. Active sites for such processes have been proposed to correspond to reduced species formed at the interface between both oxides. The present work provides direct evidence of reduced copper species located at the interface and observed during the course of near-ambient XPS experiments performed over samples of copper oxide supported on ceria nanospheres and nanocubes subjected to interaction with CO at different temperatures. The analysis of XPS results is based on DFT+U calculations employed as a complementary method for the analysis of redox properties of the catalysts and core-level shifts produced upon such redox changes. Differences observed in interfacial redox properties as a function of the ceria support morphology appear to be most useful to explain catalytic properties of this type of system for mentioned processes.

IMPROVEMENT OF PREFERENTIAL CO OXIDATION ACTIVITY OVER CUO/CO3O4-CEO2 CATALYSTS: EFFECT OF CO/CE RATIO

A series of Co3O4-CeO2 supports with different Co/Ce ratio have been synthesized by using polyethyleneglycol (PEG) as a surfactant. The catalytic performance tests indicated the activity of the catalysts is better than the corresponding support. In addition, CuO/(0.7)Co3O4-CeO2 displayed the best activity with 100% CO conversion and 93% O2 selectivity at 120 °C. Furthermore, the stability test of CuO/(0.7)Co3O4-CeO2 expressed the activity can be retained at 80% for 80h at 100 °C. Catalysts and supports were characterized by BET, XRD, TPR and TPD techniques. Discussion of the results showed that the strongest lattice distortion and the best reducibility of Co3O4-CeO2 supports were both negative factors for the catalytic activity. More precisely, an appropriate Co/Ce ratio can restrain the stronger interaction between cobalt oxide and ceria to promote the formation of reducible copper species.

Durability of Cu/SAPO-34 catalyst for NOx reduction by ammonia: Potassium and sulfur poisoning

Cu/SAPO-34 catalyst prepared by a wetness impregnation method shows better low-temperature NH3-SCR performance and higher alkali poisoning resistance than V2O5/WO3–TiO2 catalyst, but it exhibits a weaker resistance to sulfur dioxide. Both the poisoning treatments improve the high-temperature NOx conversion but decrease the low-temperature performance of Cu/SAPO-34. The textural properties and surface acidity are affected by the poisoning treatments to some extent. Nevertheless, the reducibility of copper species is suggested to be a more important factor to determine the deNOx performance of the catalysts.

Selective catalytic reduction of NO by NH3 over copper-hydroxyapatite catalysts: effect of the increase of the specific surface area of the support

The influence of the increase of the specific surface area of the support Ca-HAp on the dispersion of copper species and their activity in the NO-SCR by NH3 has been studied. The copper ion exchange does not alter the Ca-HAp structure whatever the copper concentration. The increase of the specific surface area of the support changed the dispersion and the reducibility of copper species. The high NO conversion in the whole temperature range for the catalyst with the lowest specific surface area (35 m2/g) was related to the highly dispersed CuO particles that are easily reduced. Nevertheless, the increase of the specific surface area of the support (76 m2/g), induces an increase of the size of CuO particles that become less active in NO-SCR by NH3. The addition of 2.5 % of H2O to the reaction gas feed strongly affects the NO conversion in the whole temperature range. This deactivation can be related to the change of the nature of copper species rather than to the destruction of the Ca-HAp structure.

Copper–aluminum hydrotalcite type precursors for NOx abatement

The reduction of NO by CO has been extensively studied for controlling the exhaust emissions. Most papers written on this subject have focused on supported noble metal catalysts and their drawbacks, which include their scarcity and high cost, and the tendency to form N2O as a byproduct during light-off over TWC (three-way catalyst). A copper–aluminum hydrotalcite-type precursor was successfully synthesized with metal ratio Al/(Al+Cu)=0.17, using carbonate as compensation anion. Different synthesis parameters were varied aiming to find a pure phase with high synthesis yield. The catalysts were obtained after calcination to 600°C and their performance was evaluated in NO reduction by CO. Another precursor containing hydrotalcite and malachite phases was used to compare properties and performance of the catalysts. The formation of the hydrotalcite phase in precursors and mixed oxides in the catalysts was evidenced by X-ray diffraction (XRD) and Raman spectroscopy. Redox properties were studied with TPR/TPO/TPR cycles, which show different reducible copper species for each material. The catalyst derived from pure copper–aluminum hydrotalcite-type precursor has attained an excellent performance promoting low N2O yield.

Comparison of CuO-MO x (M=Ce, Zn, Cr and Zr) catalysts in various water-gas shift reactions

The water-gas shift (WGS) reaction in the temperature range of 100–350 °C for various feed compositions simulating forward, reverse and real WGS conditions was studied for a series of coprecipitated mixed metal oxide catalysts of 30 wt% of CuO and 70 wt% of metal oxide (CeO2, ZnO, Cr2O3, and ZrO2) as well as for a commercial WGS catalyst (ICI 83-3). The catalysts were characterized using BET, XRD, H2-TPR and N2O dissociation studies. Among the tested catalysts, CuO-Cr2O3 showed the best activity in the forward WGS, while the commercial catalyst was the best catalyst in the real and reverse WGS reactions. The effect of Cu content in the catalyst was also studied and, in the case of the real WGS, 50 wt% CuO-Cr2O3 was more active than 30 wt% CuO-Cr2O3. H2 and CO2 were found to inhibit the forward WGS, decreasing the reaction rate substantially, particularly at temperatures below 200 °C. The inhibition effect varied depending on the tested catalyst and increased with increasing H2 or CO2 concentration. As the inhibition effect was reversible, the competitive adsorption of H2 or CO2 on the active sites has been suggested to be responsible for the effect. The high activity of the commercial catalyst in the H2 rich real WGS could be described by the difference in the H2 inhibition between the catalysts. An easily reducible copper species was found in CuO-Cr2O3 and could be attributed to the high activity in the forward WGS. Keywords:Mixed Metal Oxide Catalysts, Water Gas Shift Reaction, H2 Inhibition, CO2 Inhibition, Copper Chromate Catalyst

Redox properties and VOC oxidation activity of Cu catalysts supported on Ce1−xSmxOδ mixed oxides

A series of Cu catalysts supported on Ce1−xSmxOδ mixed oxides with different molar contents (x=0, 0.25, 0.5, 0.75 and 1), was prepared by wet impregnation and evaluated for volatile organic compounds (VOC) abatement, employing ethyl acetate as model molecule. An extensive characterization study was undertaken in order to correlate the morphological, structural and surface properties of catalysts with their oxidation activity. The optimum performance was obtained with Cu/CeO2 catalyst, which offers complete conversion of ethyl acetate into CO2 at temperatures as low as 260°C. The catalytic performance of Cu/Ce1−xSmxOδ was interpreted on the basis of characterization studies, showing that incorporation of samarium in ceria has a detrimental effect on the textural characteristics and reducibility of catalysts. Moreover, high Sm/Ce atomic ratios (from 1 to 3) resulted in a more reduced copper species, compared to CeO2-rich supports, suggesting the inability of these species to take part in the redox mechanism of VOC abatement. Sm/Ce surface atomic ratios are always much higher than the nominal ratios indicating an impoverishment of catalyst surface in cerium oxide, which is detrimental for VOC activity.

Selective oxidation processes of organic substances in water by means of photocatalytic systems

Selective oxidation of benzyl alcohol into benzaldehyde in anoxic acidic aqueous solution, through a TiO2/Cu(II)/solar UV photocatalytic system, has been investigated both in a laboratory scaled reactor equipped with a high-pressure mercury lamp as well as in a solar pilot plant. During the laboratory experiments, benzaldehyde gave best results, in terms of yield, equal to 35% with respect to the initial benzyl alcohol concentration. A partial conversion of benzaldehyde to benzoic acid has also been observed. Traces of hydroxylated by-products have also been detected. On the basis of the formation of these species, a production of HO radicals has been thus inferred. The study has suggested that different operative parameters, such as the composition and amount of TiO2 photocatalyst, pH, ionic inorganic components in water, and the initial concentration of Cu(II) ions, play an important role in the photocatalytic selective oxidation of benzyl alcohol. The mechanism of photocatalytic selective oxidation of benzyl alcohol into benzaldehyde and benzaldehyde into benzoic acid has been investigated in the presence of TiO2 catalyst and cupric ions, as electron acceptor, in water at a pH = 2.0 and under deaerated conditions. A competitive adsorption has been proposed in which the aromatic substrates are adsorbed on the TiO2 surface and react with the positive holes. Whereas Cu(II) ions are reduced to Cu(0) by the photogenerated electrons. A new kinetic model has been developed by writing a set of mass balance equations for the main species involved in the photocatalytic oxidation process. The resulting mathematical model has been used for the analysis of the data collected at different starting substrates’ concentrations. During each of the selective photoxidation runs, it satisfactorily predicts the concentrations of Cu(II) species, organic substrates, and intermediates. The effect of ionic components, which compete with benzyl alcohol and benzaldehyde for the reaction with positive holes on the catalyst surface and behave as scavengers towards HO radicals, has been taken into account in the model. The values of some rate constants of the reactions of the holes with benzyl alcohol, benzaldehyde, Cu(II) species, and inorganic anions (sulfates and di-hydrogenophosphates), not available in the literature, have been estimated by a proper optimizing procedure. 7 The conversion of hydroxybenzyl alcohols, methoxybenzyl alcohols and nitrobenzyl alcohol into the corresponding aldehydes has been attempted by using the same process. The presence and position of substituent groups in the aromatic alcohols structure change the photocatalytic oxidation rates and product selectivities with respect to that previously observed for unsubstituted benzyl alcohol. In particular, the presence of both electron donating (hydroxy, methoxy groups) and electron withdrawing (nitro group) on the aromatic ring of the substrate causes a detrimental effect on the selectivity of the process with respect to that of benzyl alcohol. The technical feasibility of selective photocatalytic oxidation of benzyl alcohol to benzaldehyde, in aqueous solutions and in presence of cupric ions, has been then investigated in a solar pilot plant with Compound Parabolic Collectors. Under deaerated conditions, the presence of reduced copper species has been proved by XPS analysis. The results indicated that, at the end of the process, cupric species can be easily regenerated and reused, through a re-oxidation of reduced copper that is produced during the photolytic run, with air or oxygen in dark conditions. A figure-of-merit (ACM), proposed by the International Union of Pure and Applied Chemistry (IUPAC) and based on the collector area, has been estimated, under the proposed conditions, with the aim to provide a direct link to the solar-energy efficiency independently of the nature of the system. Generally speaking, it can be considered that the lower ACM values are, the higher is the system efficiency.

TiO2/Cu(II) photocatalytic production of benzaldehyde from benzyl alcohol in solar pilot plant reactor

The technical feasibility of selective photocatalytic oxidation of benzyl alcohol to benzaldehyde, in aqueous solutions, in presence of cupric ions has been investigated in a solar pilot plant with Compound Parabolic Collectors. Aldrich (pure anatase) and P25 Degussa TiO2 have been used as photocatalysts. The influences of cupric species concentrations, solar irradiance and temperature are discussed too. The oxidation rates were strongly influenced by the initial cupric ions concentration, incident solar irradiance and temperatures.The best results found, in terms of yields and selectivities to benzaldehyde under acidic conditions were higher than 50% and 60%, respectively, under acidic conditions.Under deaerated conditions, the presence of reduced copper species was proved by XPS analysis. The results indicated that, at the end of the process, cupric species can be easily regenerated and reused, through a re-oxidation of reduced copper, produced during the photolytic run, with air or oxygen in dark conditions.A figure-of-merit (ACM), proposed by the International Union of Pure and Applied Chemistry (IUPAC) and based on the collector area, has been estimated, under the proposed conditions, with the aim to provide a direct link to the solar-energy efficiency independently of the nature of the system. Generally speaking, it can be considered that the lower ACM values the higher the system efficiency.

Ce0.97Cu0.03O2 Nanocatalysts Synthesized via Microwave-assisted Hydrothermal Method: Characterization and CO-PROX Catalytic Efficiency

ABSTRACTIn the work presented here, Ce0.97Cu0.03O2 nanoparticles were synthesized by a microwave-assisted hydrothermal method under different synthesis temperatures. The obtained nanoparticles were tested as catalysts in preferential oxidation of CO to obtain CO-free H2 (PROX reaction). The samples were characterized by X-ray diffraction, transmission electron microscopy (TEM), electron paramagnetic resonance spectroscopy (EPR) and temperature-programmed reduction (TPR). X-ray diffraction measurements detected the presence of pure cubic CeO2 for all synthesized samples. TEM images of the Ce0.97Cu0.03O2 nanoparticles revealed that samples synthesized at 80°C are composed mainly of nanospheres with an average size of 20 nm. The formation of some nanorods with an average diameter of 8 nm and 40 nm in length, and the size reduction of the nanoparticles from 20 to approximately 15 nm is observed with increasing synthesis temperature. EPR spectra indicated that copper is found well dispersed in sample synthesized at 160°C, located predominant in surface sites of ceria. For samples synthesized at 80 and 120°C, the species are less dispersed than in the other one, resulting in the formation of Cu2+−Cu2+ dimmers at the surface of ceria. TPR profiles presented two reduction peaks, one below 400°C attributed to the reduction of different copper species and a second peak around 800°C attributed to the reduction of Ce4+→ Ce3+ species located in the volume of the nanoparticles. The peak related to the reduction of copper species shifts to lower temperatures with increasing synthesis temperature, i.e., the sample synthesized at 160°C is more easily reduced than the ones synthesized at 120 and 80°C. The nanoparticles showed active as catalysts for the CO-PROX reaction. The microwave-assisted method revealed efficient for the synthesis of Ce0.97Cu0.03O2 nanoparticles with copper species selective for the CO-PROX reaction, which reaches CO conversions up to 92% for the sample synthesized at 160°C.

Enhanced Reactive Adsorption of Hydrogen Sulfide on the Composites of Graphene/Graphite Oxide with Copper (Hydr)oxychlorides

Composites of copper (hydr)oxychlorides with graphite oxide or graphene were synthesized and used as adsorbents of hydrogen sulfide at dynamic conditions at ambient temperatures. The materials were extensively characterized before and after adsorption in order to link their performance to the surface features. X-ray diffraction, FTIR, thermal analysis, TEM, SEM/EDX, and adsorption of nitrogen were used. It was found that the composite with graphene has the most favorable surface features enhancing reactive adsorption of hydrogen sulfide. The presence of moisture in the H2S stream has a positive effect on the removal process owing to the dissociation process. H2S is retained on the surface via a direct replacement of OH groups and via acid-base reactions with the copper (hydr)oxide. Highly dispersed reduced copper species on the surface of the composite with graphene enhance activation of oxygen and cause formation of sulfites and sulfates. Higher conductivity of the graphene phase than that of graphite oxide helps in electron transfer in redox reactions.

Glycerol hydrogenolysis to 1,2-propanediol with Cu/γ-Al2O3: Effect of the activation process

We have used Cu/γ-Al2O3 catalysts submitted to different activation protocols (calcination, reduction in H2/Ar, and reoxidation in N2O/N2) in order to investigate the role of the different copper surface species and acid properties in glycerol hydrogenolysis to 1,2-propanediol (1,2-PDO) under mild reaction conditions (493K, 2.4MPa H2). The activated catalysts have been characterized by temperature-programmed reduction (TPR), temperature-programmed desorption of NH3 (TPD-NH3), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance infrared Fourier transform spectroscopy of adsorbed CO (DRIFT-CO). The significant different catalytic performance obtained with the Cu/γ-Al2O3 solids is not integrally related to their acid properties, surface Cu species also participate in the glycerol conversion. Partially reduced copper species (Cu+) promotes glycerol conversion rates. Activated catalysts follow the sequence: reoxidation>reduction>calcination, when glycerol conversion is compared. Moreover, Cu species are mostly responsible for the observed 1,2-PDO selectivity values. It is strongly dependent on the Cu0/Cu+ atomic ratio and on the surface concentration of both Cu0 and Cu+ species. Accordingly, 10CuAl-c-r catalyst showed the best behavior in glycerol hydrogenolysis to 1,2-PDO.

The effect of gold on the copper-zinc oxides catalyst during the partial oxidation of methanol reaction

Hydrogen production resulting from the partial oxidation of methanol (POM) was investigated using copper-zinc-supported gold catalysts. The influence of oxygen concentration on activity and initiation temperature (T i) over Au 4.3CZ (ca. 4.3 wt.% Au, 32.3 wt.% Cu and 63.4 wt.% Zn) catalysts was compared with CZ (ca. 31.7 wt.% Cu and 68.3 wt.% Zn) catalysts. The Au 4.3CZ catalyst was able to react at temperatures lower than 195 °C, while CZ catalyst could not be initiated without pre-activation. In addition, Au 4.3CZ performed higher hydrogen selectivity and lower carbon monoxide selectivity than CZ catalyst. The addition of gold might induce a change in the reducibility of copper species and result in the more active species, Cu 0 and Cu +, on the catalytic surface and, especially, enhance the adsorption of oxygen and methoxy group at low temperature. These adsorbed oxygen atoms could be removed as CO 2, which speed up the rate-determining step of POM. It might influence initiation temperature and catalytic performance, i.e. the POM reaction can be initiated at T i: 120 °C, with catalytic performance at 95% methanol conversion, 97% hydrogen selectivity, and 5.5% carbon monoxide selectivity at 190 °C over Au 4.3CZ without pre-activation.

Catalytic reduction of NO by CO over copper-oxide supported mesoporous silica

Copper oxide supported on four different types of mesoporous silica (SBA-15, MCM-41, MCM-48 and KIT-6) were prepared and examined for catalytic reduction of NO with CO in the temperature range of 250–500 °C. Their structural and chemical properties were characterized by N 2 adsorption, low angle and wide angle X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), FTIR and temperature programmed reduction (TPR). H 2-TPR revealed that MCM-41 and SBA-15 tend to possess a higher quantity of reducible copper species in contrast to MCM-48 and KIT-6. CuO supported on MCM-41 and SBA-15 exhibited higher activity in catalytic reduction of NO than CuO supported on MCM-48 and KIT-6. The superior catalytic activity was attributed to homogeneous dispersion of CuO and availability of the reducible copper ions in the channels of mesoporous materials.

Prominent enhancement of Mn or Co addition on the performance of Cu-Ce-O catalyst used for H 2 production via dimethyl ether steam reforming

The Mn or Co promoted Cu-Ce-O catalysts were prepared by citric acid complexation, and used for the catalytic production of hydrogen via the route of dimethyl ether steam reforming (DME SR). Multiple techniques such as X-ray diffraction (XRD), X-ray absorption fine structure (XAFS), X-ray photoelectron spectra (XPS), temperature-programmed reduction by H 2 (H 2-TPR), CO-pulse chemisorption and thermal gravimetry/differential thermal analysis (TG/DTA) were employed for catalyst characterization. It is revealed by the results of XRD, XPS and XAFS that in the spent catalysts the copper species mainly exist as Cu 0 and Cu +. The addition of Co or Mn could enhance both the dispersion and the reducibility of copper species, significantly increasing the DME conversion and H 2 yield at the temperature of 400 °C or below. At higher temperature, the H 2 yield over Cu-Ce-Co-O is almost the same as that for Cu-Ce-O, due to the side reactions of CH 3OH decomposition and/or DME steam reforming to syngas. Addition of Mn to Cu-Ce-O can increase both DME conversion and H 2 yield in the whole temperature region of 300–450 °C. Much higher CO 2 selectivity is achieved over the Mn promoted catalyst. XPS and CO-pulse chemisorption results indicate that Cu-Ce-Mn-O catalyst contains more Cu + species, which determines its novel catalytic performance including higher DME conversion and higher H 2 yield.