Supported CuO Catalysts Research Articles

Structural evolution of the CuO catalyst modified with ZnO, Sn, and P promoters in the Rochow-Müller reaction

Promoters such as ZnO, Sn, and P are widely used in Cu-based catalysts for the Rochow-Müller reaction, which dominates the manufacture of organosilane monomers in the chemical industry. However, the effect of these promoters on the Cu-based catalyst structure is still unclear. In this work, we prepared a series of quartz sand (qs) supported CuO catalysts modified with ZnO, Sn, and P promoters through simple ball milling followed by calcination in air. We found that introducing these promoters can enhance the MeCl adsorption on the CuO surface, accelerating the transformation of CuO to Cu2O, then to Cu, further to CuCl, and finally to the active Cu3Si phase, leading to the improved catalytic properties with a higher dimethyldichlorosilane selectivity and Si conversion compared to the pure CuO catalyst. This work first deciphers the structural evolution of the CuO catalyst with and without ZnO, Sn, and P promoters during the Rochow-Müller reaction, which would help understand the reaction mechanism and design more efficient catalysts.

High activity of CuO/#-Fe2O3 for low temperature CO oxidation: Effect of support crystal types in catalyst design

A series of Fe2O3 supported CuO catalysts were synthesized to investigate the effect of crystal types on CO oxidation performance of CuO/Fe2O3. The catalysts were characterized with BET surface area, XRD, Raman, O2-TPD, H2-TPR, XPS and in situ DRIFTS. The results showed that the crystal types had significant impact on the performance of CuO/Fe2O3, and the CuO/γ-Fe2O3 catalyst exhibited higher catalytic activity, which corresponding to 98.5% CO conversion at 180 °C. Besides, CuO/γ-Fe2O3 displayed better reducibility, which improved the redox cycle between Fe2+ and Fe3+ species. Furthermore, the pathway of CO oxidation on CuO/Fe2O3 followed L-H mechanism. Large amount of Fe2+ species and oxygen vacancies on CuO/γ-Fe2O3 increased the oxygen activation ability, which provided more reactive oxygen species to promote the rate-determining step in CO oxidation. Moreover, carbonate species on CuO/α-Fe2O3 were prone to accumulate, which resulted in the covering of active sites on catalyst surface and inhibited the adsorption and activation of CO and O2.

CuO decorated vacancy-rich CeO2 nanopencils for highly efficient catalytic NO reduction by CO at low temperature.

With the rapid development of transportation and vehicles, the elimination of NOx and CO has highly attracted public attention. In this work, vacancy-rich CeO2 nanopencil supported CuO catalysts (CuO/CeO2-NPC) were successfully prepared for NO reduction by CO. Importantly, CeO2 with nanopencil-like shape (CeO2-NPC) have been synthesis by solvothermal method for the first time. The physicochemical properties of all samples were studied in detail by combining the means of X-ray diffraction (XRD), Raman spectroscopy, electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), H2-temperature-programmed reduction (H2-TPR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), N2 physisorption (Brunauer-Emmett-Teller), and NO and CO temperature-programmed desorption (NO-TPD and CO-TPD) techniques. Compared with CeO2 nanorods and nanoparticles supported CuO catalysts (CuO/CeO2-NR and CuO/CeO2-NP), the CuO/CeO2-NPC catalysts showed the highest catalytic activity, affording more than 90% NO conversion at 69°C as well as excellent H2O tolerance at 150°C, which is superior to catalysts previously reported. Characterization results indicated that the synergistic effect between the well-dispersed CuO and the CeO2 nanopencil support enables a favorable electron transfer between these components and enhances the density of surface oxygen vacancies and Cu+ species, which consequently accelerating the redox cycle. The results indicated that the morphology control of CeO2 support could be an efficient way to evidently enhance the catalytic performance for NO + CO reaction.

Mesoporous CuO/TiO2 catalysts prepared by the ammonia driven deposition precipitation method for CO preferential oxidation: Effect of metal loading

Supported CuO catalysts onto a highly crystalline mesoporous TiO2 material are produced via an ammonium driven deposition precipitation method and tested for preferential oxidation of CO in H2-rich gases. The effect of Cu loading on the oxidation activity is investigated by producing samples with final Cu content varying between 2.5 and 10 wt%. According to the analysis results, the chemical nature of the CuO species differs in each sample depending on the Cu loading. All materials tested are highly selective towards CO oxidation up to 160 °C. The 5 wt% Cu loaded material demonstrates the optimum CO-PROX performance, which is ascribed to the formation of finely dispersed and easily reducible copper oxide nanoparticles. Stability and durability of the latter sample are assessed by performing multiple testing cycles corresponding to >100hrs on stream as well as by the separate and combined addition of CO2 and H2O in the feeding stream.

The effect of CuO loading on different method prepared CeO2 catalyst for toluene oxidation

The support effect on CeO2 supported CuO catalysts are extensively investigated, but few studies have been reported in volatile organic compounds (VOCs) oxidation. Herein, CuO was impregnated on three conventional method synthesized CeO2 to study its impact on toluene total oxidation over CeO2 at low temperature (≤280 °C). Characterization results demonstrated that the shape and specific surface area of CeO2 affected the degree of CuO dispersion, which determine the interaction between CuO and CeO2. CuO significantly enhanced the toluene adsorption capacity of CeO2, but lots of oxygen vacancies were lost during its loading. Although strong CuCe interaction induced new oxygen vacancies, the increase or decrease of final amount was related to the original surface properties of CeO2. Mechanism analysis suggested that the activation of oxygen on oxygen vacancies controlled the toluene oxidation reaction rate. Therefore, the promotion or inhibition effect of CuO on CeO2 for toluene oxidation depends on physical and chemical properties. Through this study, we have drawn some valuable information in guiding the synthesis and design of CuO-CeO2 based catalysts.

Supported CuO catalysts on metal-organic framework (Cu-UiO-66) for efficient catalytic wet peroxide oxidation of 4-chlorophenol in wastewater

Abstract A novel heterogeneous Fenton catalyst of Cu-UiO-66 metal-organic framework (MOF) was developed for catalytic wet peroxide oxidation (CWPO) of wastewater containing the concentrated 4-chlorophenol. Cu-UiO-66 was characterized comprehensively using XRD, N2 adsorption-desorption, SEM-EDS, TEM, H2-TPR and XPS analysis to reveal its physical and chemical properties. Specifically, XPS results indicated the interaction of Cu species with framework Zr element, and H2-TPR further proved the existence of CuO active component and thermal stability of the synthesized catalysts. The Cu-UiO-66 catalysts exhibited excellent catalytic activity in the CWPO of 4-chlorophenol wastewater (1,000 to 5,000 mg/L) with conversions of 98% achieved in 20 min and complete degradation in 40 min. Based on the detailed HPLC analysis of the reaction media, mechanistic study of the CWPO of 4-chlorophenol was performed.

A γ to α type transition of CuO species over CeO2-SiO2 composites supported CuO catalysts

Abstract In this report, CeO2 nanorods and SiO2 nanospheres were mixed in various ratios and 10 wt% CuO was then impregnated onto these CeO2-SiO2 composite supports using a thermal decomposition method to prepare supported catalysts. In these composites supported catalysts, SiO2 nanospheres were used as both support and separator to enhance the dispersion and thermal stability of CeO2 nanorods and CuO catalysts. The agglomeration degree of CeO2 nanorods support significantly reduces by introducing SiO2 nanospheres in the catalyst systems, which increases the chance to expose catalytically active low-index crystal facets (110, 100, and 111) of CeO2 nanorods along with significant surface defects. Different interactions between CuO and SiO2 nanospheres, CeO2 nanorods and the CeO2-SiO2 composite supports were identified, leading to the formation of α, β, and γ-type CuO species. A continuous transition of CuO species from β and γ-type CuO on SiO2 nanospheres to α and β-type CuO on CeO2 nanorods was discovered and correlated with H2-TPR, TEM and other characterization results.

A comparative study of CO oxidation over Cu-O-Ce solid solutions and CuO/CeO2 nanorods catalysts

The distribution of copper species (on the surface or in the bulk of CeO2 support) and the interfacial interactions between CuO and CeO2 are critical in understanding the synergistic effect on the catalytic activity of CeO2 supported CuO catalysts. In this report, Cu-O-Ce solid solutions and CuO impregnated on CeO2 nanorods catalysts (CuO/CeO2) with various compositions were prepared using thermal decomposition and hydrothermal methods, to understand the distribution effect of copper species on low temperature CO oxidation. The incorporation of copper ions into CeO2 lattice in both types of catalysts was confirmed by X-ray diffraction (XRD), Raman spectroscopy, and hydrogen temperature programmed reduction (H2-TPR) analysis, indicating a strong CuO-CeO2 interfacial interaction and formation of oxygen vacancies which compensates the charge difference between copper (I/II) and cerium (III/IV) ions. A series of temperature programmed reduction-temperature programmed oxidation (TPR-TPO) thermal cycling studies were conducted to understand the interactions between three assigned copper species (α, β, and γ) with CeO2 support and the corresponding catalytic performance of the catalysts. In addition, an improved low temperature catalytic performance for the CuO/CeO2 nanorods catalysts was observed, which was attributed to stronger interactions between copper species and CeO2 nanorods enriched with surface defects (steps and voids etc.).

Peroxymonosulfate activation and pollutants degradation over highly dispersed CuO in manganese oxide octahedral molecular sieve

Manganese oxide octahedral molecular sieves (OMS-2) supported CuO catalysts were synthesized, characterized and used in the removal of Acid Orange 7 (AO7) in aqueous solution by an oxidation process involving peroxymonosulfate (PMS). It was found that the CuO species were highly dispersed in OMS-2 with a high ratio of easily reduced surface oxygen species. The synergetic effect between CuO and OMS-2 significantly improved the dye degradation rate and catalytic stability, compared with CuO, OMS-2 and supported CuO on other materials. About 97% of the dye was removed within 15min at neutral solution pH by using 0.2g/L of CuO/OMS-2 and PMS. The effect of initial solution pH, PMS concentration, reaction temperature and CuO content in the composites on AO7 degradation was also investigated. Mechanism study indicated that SO4− radicals generated from the interaction between PMS and Mn and Cu species with different oxidation states, mainly accounted for the degradation.

A novel glass fiber catalyst for the catalytic combustion of ethyl acetate

Supported CuO catalysts were prepared by wet impregnation into novel glass fiber corrugated honeycomb supports, and the catalytic combustion of ethyl acetate and the effect of copper loading were examined. Among the catalysts tested, Cu10/Al2O3-M showed the highest activity. For the catalyst, 100% conversion of ethyl acetate was achieved at 300°C, feed concentration of 1802mg/m3 and the space velocity of 5000h−1. To reveal these phenomena, the supports and catalysts were characterized by SEM, BET, XRD, H2-TPR and ethyl acetate-TPD. The catalyst activity was strongly related to the amount of highly dispersed CuO species and suitable porosity.

Oil shale ash supported CuO nanocatalysts: Preparation, characterization and catalytic activity for CO oxidation

Oil shale ash (OSA) is a solid waste, and which was generated from the shale oil production process. In this study, the OSA support CuO nanocatalyst, CuO/OSA, was prepared by using the deposition–precipitation method. The textural and structural properties of the OSA and the as-prepared CuO/OSA catalysts were characterized by the X-ray diffraction (XRD), transmission electron microscopy (TEM) and N2-sorption techniques. The catalytic activities of the as-prepared catalysts for CO oxidation were investigated by using a microreactor–GC system. The serial results indicated that this catalyst system possesses interesting catalytic performance that comparable to the previously reported metal oxide supported CuO catalysts. The 400°C calcined 8%-CuO/OSA catalyst can catalytic CO oxidation completely at 210°C. This investigation demonstrates the feasible utilization of the solid waste, which was generated from the production process of shale oil, for the control of atmospheric pollution.

Effect of an additive in a CeO2-based oxide on catalytic soot combustion

Since the emission of diesel soot damages both the environment and human health, a method for the catalytic combustion of soot at low temperatures is needed. In this study, CeO2-based oxides were investigated with respect to their catalytic activities in soot combustion to clarify the roles of ceria and an additive. The oxidation behavior of a carbon black layer over CeO2 and Al2O3 substrates in air was examined by in situ microscopy. While the carbon layer over Al2O3 gradually became thinner with an increase in temperature, it disappeared from the circumference over the CeO2 substrate. The produced gas species was also analyzed during carbon oxidation over CeO2-based catalysts containing a transition metal or rare earth oxide. Complete oxidation to CO2 was facilitated by the addition of transition metal elements to the catalysts, which could be explained by the activities of the catalysts for CO oxidation. Moreover, the effect of the support material on the carbon oxidation activity was studied for supported CuO catalysts. The reducing property of CuO over the support was related to its catalytic activity.

Effect of TiO2 crystalline phase on CO oxidation over CuO catalysts supported on TiO2

CuO catalysts supported on TiO2 with various compositions of anatase and rutile phase (CuO/R, CuOR7A3, CuOR3A7 and CuO/A) are prepared by a deposition–precipitation procedure, and products are characterized using EPR, TPR, and XPS. The oxidation of CO is used as a model reaction case to test for catalytic activity. Importantly, the type of TiO2 phase present has an effect on the physical, chemical, and catalytic properties of the CuO catalysts. The rutile phase of the TiO2 support (CuO/R) interacts weakly with the CuO and TiO2 support. Cu2+ ions in the supported-CuO are readily reduced to Cu0 during the CO oxidation reaction. Consequently, CuO/R provides large amounts of oxygen atoms for reaction with CO, which results in the highest catalytic activity among the catalysts examined. The activities of supported CuO catalysts decrease gradually with the decrease in amounts of rutile phase.

Supported CuO/γ-Al2O3 as heterogeneous catalyst for synthesis of diaryl ether under ligand-free conditions

CuO/γ-Al2O3 was employed as catalyst in the coupling reaction of iodobenzene with m-cresol to give 3-methyldiphenyl ether under ligand-free conditions. It performed more efficiently than other supported CuO catalysts (CuO/SBA-15, CuO/ZrO2, CuO/CeO2, CuO/La2O3). Reaction conditions were investigated and the yield reached 76% under the optimized terms. As a heterogeneous catalyst, CuO/γ-Al2O3 could be reused for three cycles with moderate to good yields. According to the results of XRD, TPR and XPS, the catalytic activities of supported CuO catalysts were due to the highly dispersed Cu(II) species and independent of the electronic state of these copper species.

Efficient oxidative degradation of 2-chlorophenol and 4-chlorophenol over supported CuO-based catalysts

A series of metal oxide catalysts for catalytic oxidative degradation of 2-chlorophenol (2-CP) and 4-chlorophenol (4-CP) were prepared, and the supported CuO catalysts were studied particularly. The supported CuO catalysts were characterized by XRD and NH 3-TPD techniques, in which CUO/γ-AI 2O 3 exhibited high degradation activity. The addition of Na 20 or K 2O into CUO/γ-AI 2O 3 improved the oxidative degradation of CPs remarkably, in which Na 20 was more efficient than K 2O. Over CuO/γ-Al 2O 3-Na 20, CPs were completely converted and the liberation of the inorganic chloride from 2-CP or 4-CP reached 97% or 100% respectively at 30 °C for 2 h. The supported CuO catalysts with good dispersion of CuO particles and less acid sites were favorable for the efficient oxidative degradation of CPs. In addition, the initial pH of the reaction solution was found to be an important factor which influenced the catalytic oxidative degradation of CPs and the initial pH of 11.2 and 9.8 was preferred for the oxidative degradation of 2-CP and 4-CP respectively over CUO/γ-AI 2O 3 catalyst.

Selective CO oxidation over ceria supported CuO catalysts

The effect of preparation method and pretreatment on the characteristic properties and selective CO oxidation activities of 50/50 CuO/CeO 2, 25/25/50 CuO/Co 3O 4/CeO 2 and 5/95 CuO/CeO 2 catalysts was investigated. Catalysts were characterized by BET surface area measurement, N 2 physisorption, SEM micrographs and X-ray diffraction. The selective oxidation reaction in H 2 rich stream was carried out between the 110 °C and 210 °C temperatures. The 5/95 CuO/CeO 2 catalysts gave the best CO conversion and selectivity result. The 5/95 CuO/CeO 2 catalyst calcined at 700 °C protected its activity and selectivity at 200 °C during 24 h.

CuO catalysts supported on attapulgite clay for low-temperature CO oxidation

Fiber-like high-surface-area attapulgite (APT) clay was used as a support of CuO particles, and the textural and structural properties of the prepared CuO/APT catalysts were characterized by X-ray diffraction, scanning and transmission electron microscopy, N2 sorption analysis and X-ray photoelectron spectroscopy. The catalytic behavior of the prepared CuO/APT catalysts for low-temperature CO oxidation was investigated, indicating interesting catalytic activity that comparable to the previously reported metal oxide supported CuO catalysts. Due to the unique property and the feature of much low cost and easy availability, the use of APT clay renders a great promise to be the catalyst support for the applications in various catalytic reactions including the low-temperature CO oxidation.

Effect of copper species and the presence of reaction products on the activity of methane oxidation on supported CuO catalysts

The activity of the various CuO species found in supported copper catalysts and the effect of the presence of reaction products, CO2 and H2O, was studied during the complete oxidation of methane. Series of copper catalysts supported on ZrO2, Al2O3 and SiO2 with different metal concentrations were analyzed under identical experimental conditions of reactant concentration and temperature. The catalysts were characterized by TPR, UV–vis spectroscopy and XRD. The results show that the activity of supported CuO is closely related to the kind of Cu species formed on the different supports. It was found that the Cu species formed on ZrO2 and Al2O3 are dependent on the metal loading/support's surface area ratio, and that the activity of highly dispersed Cu is substantially higher than that of bulk CuO. In the case of silica, only the formation of bulk CuO was detected, accounting for the low activity of CuO/SiO2 catalysts. The activity of highly dispersed Cu species formed on ZrO2 is higher than those formed over Al2O3, and it is not significantly affected by the formation of bulk CuO on the surface. On the contrary, the activity of copper species formed on alumina decreases continuously as the Cu loading is increased. Thus, for the range of copper loading studied in this work, the activity of the catalysts, per gram of loaded Cu, follows the sequence: CuO/ZrO2>CuO/Al2O3≫CuO/SiO2. It was also found that CO2 does not inhibits the activity of the CuO/ZrO2 catalysts, while water inhibits the combustion reaction of methane, with an estimated reaction order of about −0.2 for temperatures between 360°C and 420°C.

Regeneration of Al2O3-Coated Cordierite Supported CuO for Simultaneous SO2 and NO Removal

Al2O3-Coated cordierite supported CuO catalysts exhibit desirable activities for simultaneous SO2 and NO removal from flue gas at 400 °C. This paper aims to investigate their regeneration behavior when it is conducted in 5% NH3/Ar at 400 °C. N2 adsorption, scanning electron microscopy (SEM), temperature-programmed reduction (TPR), chemical analysis, extended X-ray adsorption fine structure (EXAFS), and X-ray diffraction (XRD) techniques are used in the study. Results show that a small amount of sulfates located in some of the pores of the catalysts cannot be reduced by NH3 at 400°C, which results in significant decreases in surface area and pore volume of the catalyst. This, in turn, reduces the mass transfer rate of SO2 and makes some of the reduced copper not reachable by SO2 in the time frame of the experiment (SO2 conversion of greater than 70%). These are responsible for the decrease in SO2 removal activity after the regeneration. Water washing of the catalyst after the first regeneration may remove ...

Preparation and Characterization of Ce0.3Ti0.7O2and Supported CuO Catalysts for NO+CO Reaction

The Ce x Ti1−x O2 mixed oxides at different mole ratios (x=0.1–1.0) were prepared by co-precipitation of TiCl4 and Ce(NO3)3. The structural and reductive properties of the Ce x Ti1− x O2 were affected by calcination temperature. At x=0.1–0.3, CeTi2O6 phase was formed and mainly as amorphous after calcination at 650°C. At x=0.3, only CeTi2O6 was formed after calcination at 750°C and CeTi2O6 crystallized completely after calcination at 800°C. TPR analyses showed that the amount of H2 consumption by Ce x Ti1−xO2 (650°C) (except x=0.1) was greater than that by single CeO2, and the valence of CeO2was the lowest (+3.18) at x=0.3. CuO/Ce0.3Ti0.7O2 was prepared by the impregnation method and catalytic properties were examined by means of a GC micro-reactor NO+CO reaction system, BET, TPR, XRD, XPS and NO-TPD. It was found that CuO/Ce0.3Ti0.7O2 calcined at 650°C had the highest activity in NO+CO reaction with 100% NO conversion at reaction temperature of 300°C, and at 650°C Ce0.3Ti0.7O2just began to crystallize. The catalytic activities were largely affected by the pre-treatment conditions. At low reduction temperature (100°C), CuO species was difficult to reduce. When high degree of reductions took place, both CuO species and Ce0.3Ti0.7O2 reduced and thus a part of CuO species on the support surface would be covered. The XPS and NO-TPD analyses showed that CuO/Ce0.3Ti0.7O2 had four NO absorption centers (Cu+, Cu2+(I), Cu2+(II) and Ce3+). The CuO species involving in NO+CO reaction included Cu2+(I) and Cu+, and CeO2 species (Ce3+ and Ce4+).