Wide Operating Temperature Window Research Articles

Superior Performance of Fe1-xWxOδ for the Selective Catalytic Reduction of NOx with NH3: Interaction between Fe and W.

Novel iron-tungsten catalysts were first developed for the selective catalytic reduction of NOx by NH3 in diesel exhaust, achieving an excellent performance with a wide operating temperature window above 90% NOx conversion from 225 or 250 to 450 °C (GHSVs of 30 000 or 50 000 h-1). It also exhibited a pronounced stability and relatively high NOx conversion in the presence of H2O, SO2 and CO2. The introduction of W resulted in the formation of α-Fe2O3 and FeWO4 species obtained by HRTEM directly. The synergic effect of two species contributed to the high SCR activity, because of the increased surface acidity and electronic property. The FeWO4 with octahedral [FeO6]/[WO6] structure acted as the Brønsted acid sites to form highly active NH4+ species. Combining DFT calculations with XPS and UV-vis results, it was found that the fine electron interaction between α-Fe2O3 and FeWO4 made the electron more easily transfer from W6+ sites to Fe3+ sites, which promoted the formation of NO2. Judging by the kinetics and SCR activity studies, the Fe0.75W0.25Oδ with an appropriate W amount showed the strongest interaction, and thereby the lowest activation energy of 39 kJ•mol-1 and optimal catalytic activity. These findings would be conducive to the reasonable design of NH3-SCR catalysts by adjusting the fabrication.

Metal-loaded ZSM5 zeolites for catalytic purification of dioxin/furans and NOx containing exhaust gases from MWI plants: Effect of different metal cations

A series of metal loaded ZSM5 including Cu/, Fe/, Mn/ and V/ was prepared and their catalytic activity, selectivity and durability were compared with the commercially used VOx/TiO2 catalyst for the combined abatement of NO and o-dichlorobenzene (o-DCB, model molecule to simulate PCDD/Fs) from the off-gases of a municipal waste incinerator (MWI) plant. Catalysts textural, acid and redox properties have been characterized by N2 adsorption–desorption isotherms, XRD, NH3-TPD and H2-TPR and a higher surface area, acidity and reducibility of the metal loaded zeolite catalysts have been confirmed. By catalytic tests carried out in the experimental conditions close to those employed in MWI plants, it was concluded that VOx/TiO2 show higher catalytic performance than metal/zeolite catalysts. A relationship between metal reducibility and the catalyst activity was found. However, zeolites due to their high acidity are less selective to NH3 oxidation reaction (negligible N2O formation) and therefore higher NO conversion is obtained in a wider operating temperature window. Using zeolites selectivity to CO is lower, although traces of trichlorobenze are detected. Both reactions are well fit to first order reaction kinetic over all the catalysts. In addition, neither of the catalysts show evidence of deactivation during 12h of reaction. Among metal/zeolites, Cu/Z is the most active catalyst, whereas Fe/Z is the less for both NO reduction and o-DCB oxidation reactions. Unfortunately, Cu/Z high selectivity to highly chlorinated compounds, like trichlorobenzene, was also found.

Porous bimetallic Mn2Co1Ox catalysts prepared by a one-step combustion method for the low temperature selective catalytic reduction of NOx with NH3

The porous Mn2Co1Ox catalysts are prepared by a one-step combustion (CB) method for low temperature deNOx process. This catalyst displays an excellent NH3-SCR activity, achieving 100% NOx conversion at 150–300°C. In addition, the catalyst shows high N2 selectivity, wide operating temperature window, high stability, and high H2O and SO2 resistance. The crystalline phase of CoMn2O4, porous structure and large specific surface areaare beneficial for the deNOx activity. The catalyst exists abundant Mn4+, Co3+ and surface adsorbed oxygen species, which improve the catalyst's redox ability. Plenty of acid sites from the strong interaction of manganese and cobalt oxide enhance the catalyst performance.

Modulating the operation temperature window of CO preferential oxidation in H2-rich gases on three dimensionally ordered macroporous CeO2–CuO catalysts by tuning their composition and incooperating Fe2O3 and Co3O4

Three dimensionally ordered (3DOM) copper-ceria based catalysts (CeO2–CuO, CeO2–CuO–Fe2O3, and CeO2–CuO–Co3O4) with diverse Ce/Cu atomic ratios and different doping amounts of Fe2O3 and Co3O4 are synthesized via a precursor thermal decomposition-assisted colloidal crystal templating method. The as-obtained CeO2–CuO, CeO2–CuO–Fe2O3 and CeO2–CuO–Co3O4 catalysts possess three dimensionally ordered macroporous structures. And their particle sizes, chemical compositions, and surface elemental states are investigated according to the variations of Ce/Cu atomic ratios and doping amounts of Fe2O3 and Co3O4. The catalytic performance of CO preferential oxidation in H2-rich gases over 3DOM CeO2–CuO, CeO2–CuO–Fe2O3, and CeO2–CuO–Co3O4 catalysts are mainly relevant to their particle sizes, chemical compositions, surface states, and synergetic interactions between different components. By modulating the Ce/Cu atomic ratios and the doping amounts of Fe2O3 and Co3O4, the superior catalytic performance of 3DOM CeO2–CuO catalysts with high CO conversion, CO2 selectivity and longer-term stability in a wide operation temperature window is achieved. This synthetic strategy provides a new methodology for the fabrication of 3DOM structured highly efficient catalysts, which would be very useful in the actual working conditions for proton exchange membrane fuel cells and water-gas shift reactions.

Low-Temperature, High Energy Density Non-Aqueous Redox Flow Battery

Redox flow battery (RFB) is a well-known storage technology. Commercial RFBs are based on aqueous electrolytes, but also several organic electrolytes are evaluated. Organic solvents provide a number of advantages due to their physicochemical properties, such as a wider operating temperature window and a wider stable potential window. Limiting factor in these systems is the solubility of the redox-active species.In our study the solubility of vanadium(III) acetylacetonate as redoxactive species and tetrabutylammonium hexafluorophosphate as supporting electrolyte were investigated in a ternary solvent mixture containing acetonitrile, 1,3-dioxolane and dimethyl sulfoxide. The solubility could be almost doubled compared to the well-known acetonitrile system [1]. Furthermore the non-aqueous redox flow battery demonstrated good performance at -25°C (Figure 1).Further studies to improve the solubility of redox-active species and to optimize battery tests are still under research. Figure 1: Energy efficiency (EE) and coulombic efficiency (CE) of the V(acac)3 RFB in acetonitrile-1,3-dioxolane-dimethyl sulfoxid solvent mixture at -25°C. Literature:[1] Shinkle, A. A.; Sleightholme, Alice E. S.; Griffith, L. D.; Thompson, L. T.; Monroe, C. W., Journal of Power Sources 206 (2012) 490–496.

A Remarkable Catalyst Combination to Widen the Operating Temperature Window of the Selective Catalytic Reduction of NO by NH3

AbstractOn the basis of the idea of combining high selective catalytic reduction (SCR) activity, high N2 selectivity, and broad operating temperature window, we developed a combined catalyst process that was found to be a convenient way to design a highly efficient SCR process for NO with NH3. The single catalysts of MnOx–CeO2/TiO2 and V2O5–WO3/TiO2 as well as combined catalysts with different configurations were fully characterized by XRD, temperature‐programmed reduction of H2, and temperature‐programmed desorption of NO/O2. In addition, they were tested for the oxidation of NO or NH3 as well as the SCR of NO with NH3. The correlations between combining configurations and SCR activity results were also revealed. Furthermore, fundamental evidences were given for the rational design of the process and its efficiency maximization (assembly order and catalytic bed volume). An adequate configuration, with MnOx–CeO2/TiO2 and V2O5–WO3/TiO2 active materials, ensures an excellent SCR performance (NO conversion >85 %, N2 yield >70 %, and decreased N2O production) over a wide operating temperature window (from 150 to 400 °C).

高比能超级电容器的研究进展

Compared with traditional batteries, supercapacitors exhibit the high power density, long cycle life and wide operating temperature window. However, the relatively low energy density of supercapacitor still remains a challenge. In this paper, the structure, classification and development of supercapacitors are introduced, with an emphasis on recent work in high performance supercarpacitors of our group. The strategy for enhancement of energy density is to increase the voltage window of symmetric carbon-based supercapacitors using neutral, organic, and ionic liquid electrolytes, and adopt asymmetric supercapacitors in which one electrode is pseudocapacitive while the other utilizes double layer capacitance. Briefing is also presented on our recent investigation into hybrid supercapacitor with electrode material of lithium-ion battery/activated carbon as positive electrode, and graphite as negative electrode. This paper is ended by a perspective of future development of supercapacitors.

High deNOx performance of Mn/TiO 2 catalyst by NH 3

The deNOx performance of the s-Mn/TiO 2 catalyst prepared by sol–gel method has been significantly enhanced, particularly in the low temperature region. Mn is basically incorporated into the matrix of Ti and becomes a structural component of s-MnO 2/TiO 2 mixed oxide, whereas by impregnation method it simply exists on the surface of i-Mn/TiO 2. The well-dispersed Mn over s-Mn/TiO 2 catalyst is the primary cause for the high deNOx performance compared to that over i-Mn/TiO 2. The addition of Fe onto the Mn/TiO 2 catalyst improves the NOx removal activity by NH 3 in a wide operating temperature window, including the low temperature region less than 250 °C, regardless of the catalyst preparation methods. Including NO 2 (NO 2/NO = 1) in the feed gas stream further enhances the low temperature deNOx activity of Mn/Fe/TiO 2 catalyst.

An investigation into catalysts to improve low temperature performance in the selective catalytic reduction of NO with NH3

Selective catalytic reduction with NH3 is considered one of the most effective technologies controlling NOx emission. Metal Fe-based catalysts were used in the investigation to improve low temperature performance of NOx conversion. The temperature range studied was between 150°C and 350°C in increments of 50°C. The honeycomb catalysts were prepared by an impregnation method. The study also included characterisation of catalysts by BET, XRD, H2-TPR and XPS methods.It was found that an increase in metal Fe content from 2 to 6% wt offered an improvement in the catalytic performance. However, a further increase in Fe content resulted in a decrease in its performance. More than 90% NOx conversion rate could be achieved over the Fe-based honeycomb catalyst at a low temperature by doping with different weights of Ni and Zr metals. Amongst all the catalysts studied, the mixed metal catalyst of Fe-Ni-Zr was the one with most potential. This was because of its higher NOx conversion rate at a low temperature and also because of its wider operating temperature window. The effect of gas hourly space velocity (GHSV) was also investigated and the results showed that as GHSV increased, the reduction of NOx decreased.

Selective catalytic reduction of NO x by H 2 using proton conductors as catalyst supports

The selective catalytic reduction (SCR) of NO x by H 2 was studied using proton-conducting Sn 0.9In 0.1P 2O 7 as a catalyst support at 50–350 °C. When a mixture of 800 ppm NO, 1400–8400 ppm H 2, and 5% O 2 in Ar was introduced to the Pt/C working electrode, NO x was reduced to N 2 with N 2 selectivity values > 80 % . The reaction mechanism was shown to be based on a mixed potential at the Pt/C working electrode. This mechanism was also applicable to a Sn 0.9In 0.1P 2O 7-supported Pt catalyst. H 2 SCR over the Pt/Sn 0.9In 0.1P 2O 7 catalyst was characterized by a wide operating temperature window (50–350 °C) and remarkable N 2 selectivity values ( > 80 % ). Catalyst performance could be further improved by the addition of Rh to Pt, in which NO x conversion was a maximum 1.4 times higher than that over the Pt/Sn 0.9In 0.1P 2O 7 catalyst and N 2 selectivity was increased to > 89 % at all temperatures tested.

Selective Catalytic Reduction of Nitric Oxide with Propene and Diesel Fuel as Reducing Agents over Anodic Alumina Catalyst

A novel metallic monolith anodic γ-alumina catalyst, prepared through anodization of aluminum, hot water treatment and active metal impregnation, was employed to investigate the selective catalytic reduction of NO under oxygen-rich conditions with propene and diesel fuel as reducing agents.Using propene as a reducing agent, Pt/Al2O3/Al offered the best low-temperature SCR activity (about 573 K), and was resistant to SO2 poisoning. However, a high undesired selectivity to N2O and a narrow operating-temperature window were two major disadvantages. At a moderate temperature (about 673 K), Cu-Ce/Al2O3/Al showed a favorable de-NOx activity comparable to Pt/Al2O3/Al, a higher N2 selectivity and a wider operating-temperature window than Pt/Al2O3/Al. In particular, adding SO2 into feedstream dramatically promoted the de-NOx activity of Cu-Ce/Al2O3/Al, and this increase was unchanged with time-on-stream. Among the catalysts tested in this paper, the highest de-NOx activity was obtained on the alumite support, but at a high temperature (about 773 K). Although the presence of SO2 strongly inhibited the NOx reduction of the alumite support, NOx conversion of 80% could still be maintained in the coexisting SO2 and H2O.When introducing diesel fuel instead of propene as a reducing agent, the over-oxidation of diesel fuel by oxygen remarkably decreased the NOx reduction of Pt/Al2O3/Al and Cu-Ce/Al2O3/Al. The alumite support became a promising choice, due to the stable 67% of de-NOx activity achieved under the same redox conditions. However, the presence of a high concentration of SO2 substantially depressed the de-NOx activity of the alumite support. On the contrary, a significant promotional effect of SO2 on the de-NOx activity was also observed over Cu-Ce/Al2O3/Al, when using diesel fuel as a reducing agent, as observed in the SCR-NO-C3H6.

Control of NOxEmissions from Diesel Engine by Selective Catalytic Reduction (SCR) with Urea

Among the catalysts screened, Cu-ion exchanged ZSM5 zeolite exhibited the highest NO removal activity, particularly at low reaction temperatures below 200 °C, maintaining a wide operating temperature window. The hydrothermal stability of the CuZSM5 catalyst can be improved by the optimization of metal content of the catalyst. Through the variation of reactor operating conditions, NO conversion of better than 90% could be achieved with a minimum NH3 slip. The decomposition of urea was also examined and a kinetic model for both thermal and catalytic decomposition of urea was developed. Urea-SCR over the CuZSM5 catalyst exhibited that the NO removal activity is competitive to that by NH3-SCR, indicating urea can be effectively utilized in SCR reactor system as the reducing agent.