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1.
In this essay, the effect of the morphology of the CeO2 support and the Ba promoter on the ammonia synthesis reaction was studied. CeO2 support with {110} and {100} crystal planes and more oxygen vacancies enhanced the catalytic activity of ammonia synthesis. The relatively uniform microspheres structure CeO2 support (CeO2-MS) with {110} and {100} crystal planes was synthesized. The structural functions of the as-synthesized CeO2 support for the Ru-based catalyst were investigated in the ammonia synthesis reaction. The results of catalytic performance showed that the catalytic activity of 2.5%Ru/CeO2-MS catalyst reached 8940 μmol· g?1· h?1 at 450 ℃, 3.8 MPa, H2/N2 = 3 (60 mL?min?1), which is higher nearly 2.5 times than the 2.5%Ru/CeO2-commercial (CeO2-C). And the catalytic activity of catalysts increased with the increase of reaction temperature. The activity of 6%Ba-2.5%Ru/CeO2-MS (24000 μmol· g?1· h?1) catalyst increased about 268% than that of catalyst without addition of Ba. Their physical and chemical properties were characterized by XRD, BET, HRTEM, H2-TPR, H2-TPD, and XPS analyses. Our results indicate that the 2.5%Ru/CeO2-MS catalyst and catalysts involving promoters (Cs, K, and Ba) exhibit significant support-morphology-dependent catalytic activity for ammonia synthesis.  相似文献   

2.
Electrochemical evaluation of the RuxMySez (M = Cr, Mo, W) type electrocatalysts towards the oxygen reduction reaction (ORR) is presented. The electrocatalysts were synthesized by reacting the corresponding transition metal carbonyl compounds and elemental selenium in 1,6-hexanediol under refluxing conditions for 3 h. The powder electrocatalysts were characterized by scanning electron microscopy (SEM), and X-ray diffraction (XRD). Results indicate the formation of agglomerates of crystalline particles with nanometric size embedded in an amorphous phase. The particle size decreased according to the following trend: RuxCrySez > RuxWySez > RuxMoySez. Electrochemical studies were performed by rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) techniques. Kinetic parameters exhibited Tafel slopes of 120 mV dec−1; exchange current density of around 1 × 10−5 mA cm−2 and apparent activation energies between 40 and 55 kJ mol−1. A four-electron reduction was found in all three cases. The catalytic activity towards the ORR decreases according to the following trend: RuxMoySez > RuxWySez > RuxCrySez. However this trend was not maintained when the materials were tested as cathode electrodes in a single polymer exchange membrane fuel cell, PEMFC. The RuxWySez electrocatalyst showed poor activity compared to RuxMoySez and RuxCrySez which were considered suitable candidates to be used as cathode in PEMFCs.  相似文献   

3.
A LiOH-promoted Ru-based catalyst was recently reported to have a high TOF of 17.7 s−1 at 623 K, compared to 2.7 s−1 for an un-promoted Ru-based catalyst, and has been reproduced for this study to develop further understanding of the catalyst activity under a range of conditions. The kinetic values were calculated using a Temkin-Pyzhev-like power law rate expression model. Reaction orders, pre-exponential factors (A) and activation energies (E) were calculated for two temperature ranges, 623–748 K, and 748–873 K. The TOF of this catalyst at 623 K is not similar to that previously reported, being only 1.6 s−1 in this study. A follow-up CFD analysis supports the fact that the kinetic model effectively describes performance of the catalyst at a range of temperatures and pressures, and can be used in the future on similar catalysts. H2 partial pressure has an inhibitory effect on the rate of decomposition of NH3 at all temperatures, not just near or below 673 K as previously proposed in the literature, however equilibrium decomposition is still possible with sufficient catalyst loading.  相似文献   

4.
    
Developing efficient but facile strategies to modulate the catalytic activity of Ru deposited on metal oxides is of broad interest but remains challenging. Herein, we report the oxygen vacancies and morphological modulation of vacancy-rich Co3O4 stabilized Ru nanoparticles (NPs) (Ru/VO-Co3O4) to boost the catalytic activity and durability for hydrogen production from the hydrolysis of ammonia borane (AB). The well-defined and small-sized Ru NPs and VO-Co3O4 induced morphology transformation via in situ driving VO-Co3O4 to 2D nanosheets with abundant oxygen vacancies or Co2+ species considerably promote the catalytic activity and durability toward hydrogen evolution from AB hydrolysis. Specifically, the Ru/VO-Co3O4 pre-catalyst exhibits an excellent catalytic activity with a high turnover frequency of 2114 min?1 at 298 K. Meanwhile, the catalyst also shows a high durability toward AB hydrolysis with six successive cycles. This work establishes a facile but efficient strategy to construct high-performance catalysts for AB hydrolysis.  相似文献   

5.
    
Developing efficient modulation strategies to upgrade the catalytic activity and reusability of Rh-catalyzed hydrogen evolution from ammonia borane (AB) hydrolysis are definitely profitable but remains a grand challenge. Here, we develop a stepwise activation strategy to produce highly active and reusable Rh/CoFe2O4-SB-H2 with abundant oxygen vacancies and strong electronic metal-support interaction through stepwise reduction of Rh/CoFe2O4 precursor using sodium borohydride and H2 as the reducing agents. Under ultrasonic irradiation, Rh/CoFe2O4-SB-H2 with an ultralow Rh loading of 0.20 wt% can be utilized as an excellent catalyst for hydrogen production from room-temperature AB hydrolysis with a high turnover frequency (TOF) of 1894 min−1. The TOF value could be further promoted to 15,570 min−1 in the alkaline ultrasonic environment. The catalyst has a superior reusability with 75% maintaining activity of initial one in the 10th cycle. The strong electronic metal-support interaction, rich oxygen vacancies and ultrasound irradiation promote the oxidative cleavage of the O–H bonds in attracted H2O and thus account for high performance toward hydrogen production from AB. This catalyst can also be utilized as an active catalyst for oxygen generation from H2O2 decomposition. The developed strategies can be applied to upgrade the performance of other reducible metal oxides supported metal catalysts toward catalytic applications.  相似文献   

6.
Due to its poor electrical conductivity and finite exposed active sites, the development of high activity Co3O4 oxygen evolution reaction (OER) electrocatalysts remains a major challenge. Oxygen vacancies can enhance the electrical conductivity of electrocatalysts and reduce the adsorption energy of H2O molecules on surfaces, thereby significantly enhancing their electrocatalytic activity. Taking inspiration from this, we demonstrate a green and facile reduction strategy to prepare reduced Co3O4 nanosheet arrays (R-Co3O4 NSA) with large electrochemical surface area and rich in surface oxygen vacancies. Compared to pristine Co3O4 nanosheet arrays (P-Co3O4 NSA), R-Co3O4 NSA exhibits better OER performance, with a lower overpotential of 330 mV at a current density of 20 mA cm?2 and a smaller Tafel slope of 72 mV dec?1. Impressively, the excellent properties of R-Co3O4 NSA can rival to the state-of-the-art noble metal oxide electrocatalyst (IrO2). This strategy of defect-engineering offers a briefness and cost-effective means for the development of highly efficient OER systems.  相似文献   

7.
In this report, for the first time, it has been observed that proton-conducting oxide BaZr0.1Ce0.7Y0.2O3?δ (BZCY) has significant promotion effect on the catalytic activity of Ni towards ammonia synthesis from hydrogen and nitrogen. Renewable hydrogen can be used for ammonia synthesis to save CO2 emission. By investigating the operating parameters of the reaction the optimal conditions for this catalyst were identified. It was found that at 620 °C with a total flow rate of 200 mL min?1 and a H2/N2 mol ratio of 3, an activity of approximately 250 μmol g?1 h?1 can be achieved. This is ten times larger than that for the unpromoted Ni catalyst under the same conditions although the stability of both catalysts in the presence of steam was not good. The specific activity of Ni supported on proton-conducting oxide BZCY is approximately 72 times higher than that of Ni supported on non-proton conductor MgOCeO2. These promotion effects were suspected to be due to the proton conducting nature of the support. Therefore it is proposed that the use of proton conducting support materials with highly active ammonia synthesis catalysts such as Ru and Fe will provide improved activity of at lower temperatures.  相似文献   

8.
上世纪90年代,KBR将新型钌基催化剂成功应用于氨合成工业生产,并且形成以钌基催化剂为核心的KAAP工艺。钌基催化剂由于其远高于铁基催化剂的活性特征,已经在提高产量、降低能耗方面显示出无可比拟的优越性能。钌基催化剂作为氨合成第二代催化剂,与铁基催化剂相比,具有活性高,使用寿命长,操作条件相对缓和等优点,国内已经开发成功,但未见工业化应用报道。针对某大型氨厂氨合成回路扩能改造,提出对现有3个合成塔中的第三塔进行改造,改造后第三塔装填钌基催化剂,催化剂床层由一个增加为两个,床层之间有换热器。应用模拟软件Aspen Plus对该方案进行模拟研究,并与现有改造方案进行对比分析。结果表明,本方案在不新增合成塔数量的前提下,即可实现提高液氨产能35%的目标;改造后的3个合成塔运行参数满足工业生产要求,钌基催化剂在较高氨含量下仍然表现出优异的活性;与现有新增合成塔的改造方案相比,本改造方案在成本方面具有较大的经济优势。  相似文献   

9.
Oxygen vacancy, as a kind of self-doping strategy, has been considered by numerous researchers. Several papers have been published about introducing oxygen vacancies in the semiconductors, which give a viewpoint that the concentration of oxygen vacancies may influence the performance. But few of them focus on how to control the concentration of oxygen vacancies, and how to achieve the goal without using additional equipment (such as sealed tube furnace) for too long time (20 min–4 h without considering the time for rising temperature and cooling). In this paper, oxygen vacancies were introduced into the WO3 vertically plate-like arrays films in a short time by chemical reduction. TiCl3 solutions with different concentrations were used as the reductant, and the concentration of oxygen vacancies of WO3 was proportional to the concentration of TiCl3. After importing oxygen vacancies, WO3 film photoanode showed enhanced photoelectrochemical performance, and the photocurrent of treated WO3 (0.88 mA/cm2 at 1.2 V vs. Ag/AgCl) was 1.27 times that of pristine WO3 (0.69 mA/cm2). However, the photocurrent decreased when the concentration of TiCl3 was too high. The over importation of oxygen vacancies might result in a thicker disorder layer with surface defects and more recombination centers. In such a situation, there was an unsatisfactory transfer and separation ability of photogenerated charges. This study provides new insight into controlling the concentration of oxygen vacancies via a rapid and easy approach.  相似文献   

10.
    
The performance of K and Fe loaded ZrO2 species (FeK/ZrO2) for CO2 hydrogenation was relevant to the concentration of oxygen vacancies due to the differences of ZrO2 crystal phases. The K and Fe were deposited on the surface of monoclinic zirconia (m-ZrO2) and tetragonal zirconia (t-ZrO2) with the Fe loading of 0–20 wt% and the K loading of 1 wt% by impregnation methods. The ZrO2 served as both a support and a co-catalyst for CO2 hydrogenation, exhibiting 40.54% CO2 conversion and 14.98% light olefins selectivity over the 10Fe1K/m-ZrO2 with 10 wt% Fe and 1 wt% K, at 2.0 MPa and 340 °C. Such CO2 conversion were almost 200% higher than that of 10Fe1K/t-ZrO2. The better activity of 10Fe1K/m-ZrO2 is mainly attributed to the higher concentration of oxygen vacancies on the surface of m-ZrO2 after the reduction in H2/N2. However, covering the surface of m-ZrO2, excess surface Fe species lowered the concentration of surface oxygen vacancies for reduced 10Fe1K/t-ZrO2, which inhibited the catalytic performance of ZrO2 for CO2 conversion. These investigations may propel the utilization of Zr-based catalysts on CO2 hydrogenation to various value-added chemicals.  相似文献   

11.
    
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12.
    
In this work, the solution plasma-assisted method was used to prepare NiMnAl-LDO (layered double oxides) catalysts with different treatment times, which were used for the CO2 methanation reaction. Solution plasma treatment can enhance the dispersibility of the catalyst, create oxygen defects and improve the chemical adsorption capacity of the catalyst. The results show that the low-temperature activity of the catalyst has been improved after the solution plasma treatment. We demonstrate that the NiMnAl-LDO-P(20) catalyst with high dispersion has the highest catalytic activity in CO2 methanation (81.3% CO2 conversion and 96.7% CH4 selectivity at 200 °C). Even though working for 70 h, the catalyst is still highly stable. This work provides a great promise for improving the low-temperature activity of Ni-based catalysts.  相似文献   

13.
    
On-site produced hydrogen from ammonia decomposition can directly fuel solid oxide fuel cells (SOFCs) for power generation. The key issue in ammonia decomposition is to improve the activity and stability of the reaction at low temperatures. In this study, proton-conducting oxides, Ba(Zr,Y) O3-δ (BZY), were investigated as potential support materials to load Ni metal by a one-step impregnation method. The influence of Ni loading, Ba loading, and synthesis temperature, of Ni/BZY catalysts on the catalytic activity for ammonia decomposition were investigated. The Ni/BZY catalyst with Ba loading of 20 wt%, Ni loading of 30 wt%, and synthesized at 900 °C attained the highest ammonia conversion of 100% at 600 °C. The kinetics analysis revealed that for Ni/BZY catalyst, the hydrogen poisoning effect for ammonia decomposition was significantly suppressed. The reaction order of hydrogen for the optimized Ni/BZY catalyst was estimated as low as ?0.07, which is the lowest to the best of our knowledge, resulting in the improvement in the activity. H2 temperature programmed reduction and desorption analysis results suggested that a strong interaction between Ni and BZY support as well as the hydrogen storage capability of the proton-conducting support might be responsible for the promotion of ammonia decomposition on Ni/BZY. Based on the experimental data, a mechanism of hydrogen spillover from Ni to BZY support is proposed.  相似文献   

14.
    
Hydrogen is expected to be an alternative energy carrier in the future. High-pressure hydrogen storage option is considered as the best choice. However, spontaneous ignition tends to occur if hydrogen is suddenly released from a high-pressure tank into a tube. In order to improve the safety of hydrogen application, an experimental investigation on effects of CO2 additions (5%, 10% and 15% volume concentration) on the spontaneous ignition of high-pressure hydrogen during its sudden expansion inside the tube has been conducted. Pressure transducers are used to record the pressure variation and light sensors are employed to detect the possible spontaneous ignition. It is found that the shock wave overpressure and the mean shock wave speed are almost the same inside the tube for different CO2 additions under the close burst pressures. For cases with more CO2 additions, the ignition detected time is longer and the average speed of the flame, the maximum value of light signals and the detected duration time of spontaneous ignition are smaller. It is shown that minimum burst pressure required for spontaneous ignition increase 1.47 times for 15% CO2 additions. The minimum burst pressure required for spontaneous ignition increases from 4.37 MPa (0% CO2) up to 6.41 MPa (15% CO2). With the increasing of CO2 additions, it requires longer distance and longer time for hydrogen and oxygen to mix and thus longer ignition delay distance/time. The results showed that additions of CO2 to air have a good suppressing effect on hydrogen spontaneous ignition.  相似文献   

15.
Active and durable oxygen reduction reaction (ORR) catalysts are of utmost importance to realize the commercialization of hydrogen fuel cells and metal-air batteries. Al-substituted MnFe2O4-based ternary oxide and reduced graphene oxide (MAF-RGO) nanocomposite is synthesized using an in-situ co-precipitation followed by a hydrothermal process and verified for ORR electrocatalysis in the alkaline electrolyte (0.1 M KOH). MAF-RGO is first analyzed using physicochemical characterization tools including X-ray diffraction, Raman spectroscopy, sorption studies, electron microscopy, X-ray photoelectron spectroscopy, etc. Further, the characteristic ORR peak centered at 0.56 V vs. reversible hydrogen electrode (RHE) in cyclic voltammetry (CV) studies confirms the electrocatalytic performance of MAF-RGO. The ORR onset potential of 0.92 V vs. RHE is obtained in linear sweep voltammetry (LSV) measurement at 1600 rpm in O2-saturated electrolyte exhibiting an improved ORR performance as compared to the commercial electrocatalyst. The reduction kinetics is observed to follow the desirable near 4-e- mechanism. In addition, the electrocatalyst exhibits improved relative current stability of 86% and methanol poisoning resistance of 82%, which is better in comparison to the standard Pt/C. The observed electrochemical performance results from the synergism between the oxygen vacancy-rich Al-substituted metallic oxide active species and the functional group enriched predominantly mesoporous RGO sheets with excellent electrical conductivity. The introduction of metallic species enhanced the inter-planar spacing between graphitic sheets easing the maneuver of reactant species through the electrocatalyst and accessing more ORR-active sites. This study establishes the potency of mixed transition metal oxide/nanocarbon composites as durable high-performance ORR-active systems.  相似文献   

16.
    
Selective CO methanation from H2-rich stream has been regarded as a promising route for deep removal of low CO concentration and catalytic hydrogen purification processes. This work is focused on the development of more efficient catalysts applied in practical conditions. For this purpose, we prepared a series of catalysts based on Ru supported over titania and promoted with small amounts of Rh and Pt. Characterization details revealed that Rh and Pt modify the electronic properties of Ru. The results of catalytic activity showed that Pt has a negative effect since it promotes the reverse water gas shift reaction decreasing the selectivity of methanation but Rh increases remarkably the activity and selectivity of CO methanation. The obtained results suggest that RuRh-based catalyst could become important for the treatment of industrial-volume streams.  相似文献   

17.
Water splitting is an environmentally friendly method of hydrogen generation. However, it is severely limited by the slow anodic oxygen evolution reaction (OER). Iron-nickel layered double hydroxides (FeNi LDH) are promising electrocatalysts for OER, but their intrinsically low electrical conductivity and activity limit the practical applications. Herein, chromium-doped FeNi LDH nanoarrays in situ vertically grown on the surface of the Ti3C2Tx MXene (Cr-FeNi LDH/MXene) are successfully synthesized. Remarkably, the robust interaction and electrical coupling between Cr–FeNi LDH and MXene, as well as conspicuous charge transfer and the oxygen vacancies optimizing the adsorption free energy of intermediates, equip the nanocomposites with brilliant catalytic activity and stability toward OER. Thus, the optimized Cr–FeNi LDH/MXene shows a considerable boost in the OER, which affords low overpotential (232 mV at 10 mA cm?2) and excellent durability. This work offers a new path to designing highly efficient and earth-abundant catalysts for water splitting and beyond.  相似文献   

18.
Pd0.5NixSe(0.5−x) electrocatalysts with different chemical composition, X = 0.25, 0.35, 0.45, were synthesized by a NaBH4 reduction of PdCl2, NiCl2 and SeO in a THF solution and evaluated for the oxygen reduction reaction (ORR) in acid media by electrochemical techniques of rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE). The electrocatalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and CO adsorption/stripping. The relation of Se to Ni in the samples has a profound effect on the nature of the cathode catalytic activity toward the oxygen reduction process, enhanced as the Se content in the electrocatalysts was reduced. Electrochemical results show that the ORR takes place by a multi-electron charge transfer process (n = 4e) with the formation of less than 1% of hydrogen peroxide. The enhanced activity was attributed to the high active surface area deduced from CO adsorption/stripping analysis. The research activities are reported within the focus on the activity-stability of the bimetallic chalcogenides electrocatalysts.  相似文献   

19.
    
The present work signifies the impact of doping-induced oxygen vacancies, the formation of heterojunction, and the role of Tb4+/Tb3+ redox centers on the photo-activity of Sm-ZnO/Y–Tb2O3 composite. The generation of oxygen vacancies in the produced materials is explained by PL, FTIR, and XRD analyses as a result of distortion in the local framework of oxygen ions around Zn and Tb ions. Under simulated sunlight irradiation, the Sm-ZnO/Y–Tb2O3 catalyst demonstrates efficient photocatalytic activity, obtaining an apparent amount of 21,270 mol g−1 h−1, which is around 60 times greater than that obtained over ZnO. The Sm-ZnO/Y–Tb2O3 catalyst also manifests strong stability. The generation of oxygen vacancies, the effective role of Tb4+/Tb3+ redox centers, the design of heterojunction, and high specific surface area are the responsible factors for the increased optical response, spatial separation, and fast transport of charge carriers and large density of catalytic sites to boost the H2 evolution performance. The present study can deepen the knowledge of the design and construction of novel heterosystems with strong photocatalytic aptitudes.  相似文献   

20.
    
Electrochemical ammonia synthesis from N2 under mild condition is considered a promising strategy to store energy produced by renewable sources, but it is affected by the lack of efficient catalysts for nitrogen reduction. In this work Fe-based nanoparticles with different morphology are deposited on carbon cloth via drop-casting and chemical reduction. The catalyst activity has been evaluated by cyclic voltammetry and chronoamperometry, using a 0.01 M phosphate buffered electrolyte (PBS). The produced ammonia has been determined through the indophenol method. As effective strategy to improve the catalytic activity, the morphology and particle size have been optimized and an electrochemical activation procedure has been implemented. Activation increases the available active sites and is related to higher amount of oxygen vacancies and Fe+2/Fe+3 ratio. Catalysts with optimized morphology produce ammonia at −0.35 V vs RHE with yield of 26.44 μg mgcat−1h−1 and Faradaic efficiency of 20.4%, more than five times higher than without activation.  相似文献   

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