Zirconia-Based Compositions for Use in Passive NO\u3csub\u3ex\u3c/sub\u3e Adsorber Devices

A passive NOx adsorbent includes: palladium, platinum or a mixture thereof and a mixed or composite oxide including the following elements in percentage by weight, expressed in terms of oxide: 10-90% by weight zirconium and 0.1-50% by weight of least one of the following: a transition metal or a lanthanide series element other than Ce. Although the passive NOx adsorbent can include Ce in an amount ranging from 0.1 to 20% by weight expressed in terms of oxide, advantages are obtained particularly in the case of low-Ce or a substantially Ce-free passive NOx adsorbent

Pt/CexPr1−xO2 (x = 1 or 0.9) NOx storage–reduction (NSR) catalysts

Model Pt/Ce0.9Pr0.1O2 and Pt/CeO2 NOx storage–reduction catalysts were prepared via nitrate calcination, co-precipitation and carbon-templating routes. Raman spectroscopic data obtained on the catalysts indicated that the introduction of praseodymium into the ceria lattice increased the concentration of defect sites (vacancies), arising from the higher reducibility of the Pr4+ cation compared to Ce4+. For the Pr-promoted samples, H2-TPR profiles contained high temperature bulk reduction peaks which were less pronounced compared with their ceria analogs, indicating that the presence of praseodymium enhances oxygen mobility due to the creation of lattice defects. Under lean-rich cycling conditions, the cycle-averaged NOx conversion of the Pt/Ce0.9Pr0.1O2 samples was in each case substantially higher than that of the Pt/CeO2 analog, amounting to a difference of 10–15% in the absolute NOx conversion in some cases. According to DRIFTS data, a double role can be assigned to Pr doping; on the one hand, Pr accelerates the oxidation of adsorbed NOx species during the lean periods. On the other hand, Pr doping destabilizes the adsorbed NOx species during the rich periods, and the kinetics of nitrate decomposition are faster on Pt/Ce0.9Pr0.1O2, leading to improved catalyst regeneration. These results suggest that ceria-based mixed oxides incorporating Pr are promising materials for NOx storage–reduction catalysts intended for low temperature operation.The financial support of Generalitat Valenciana (predoctoral stay BEFPI/2012), the Spanish Ministry of Economy and Competitiveness (Project CTQ2012-30703), and co-financing by FEDER resources is acknowledged. Partial financial support was also provided by the National Science Foundation and the U.S. Department of Energy (DOE) under award no. CBET-1258742

Effect of Cu and Sn promotion on the catalytic deoxygenation of model and algal lipids to fuel-like hydrocarbons over supported Ni catalysts

The ability of Cu and Sn to promote the performance of a 20% Ni/Al2O3 catalyst in the deoxygenation of lipids to fuel-like hydrocarbons was investigated using model triglyceride and fatty acid feeds, as well as algal lipids. In the semi-batch deoxygenation of tristearin at 260 °C a pronounced promotional effect was observed, a 20% Ni-5% Cu/Al2O3 catalyst affording both higher conversion (97%) and selectivity to C10-C17 alkanes (99%) in comparison with unpromoted 20% Ni/Al2O3 (27% conversion and 87% selectivity to C10-C17). In the same reaction at 350 °C, a 20% Ni-1% Sn/Al2O3 catalyst afforded the best results, giving yields of C10-C17 and C17 of 97% and 55%, respectively, which contrasts with the corresponding values of 87 and 21% obtained over 20% Ni/Al2O3. Equally encouraging results were obtained in the semi-batch deoxygenation of stearic acid at 300 °C, in which the 20% Ni-5% Cu/Al2O3 catalyst afforded the highest yields of C10-C17 and C17. Experiments were also conducted at 260 °C in a fixed bed reactor using triolein − a model unsaturated triglyceride − as the feed. While both 20% Ni/Al2O3 and 20% Ni-5% Cu/Al2O3 achieved quantitative yields of diesel-like hydrocarbons at all reaction times sampled, the Cu-promoted catalyst exhibited higher selectivity to longer chain hydrocarbons, a phenomenon which was also observed in experiments involving algal lipids as the feed. Characterization of fresh and spent catalysts indicates that Cu enhances the reducibility of Ni and suppresses both cracking reactions and coke-induced deactivation

Differential Seroprevalence of Human Bocavirus Species 1-4 in Beijing, China

BACKGROUND: Four species of human bocaviruses (HBoV1-4) have been identified based on phylogenetic analysis since its first report in 2005. HBoV1 has been associated with respiratory disease, whereas HBoV2-4 are mainly detected in enteric infections. Although the prevalence of HBoVs in humans has been studied in some regions, it has not been well addressed globally. METHODOLOGY/PRINCIPAL FINDINGS: Cross-reactivity of anti-VP2 antibodies was detected between HBoV1, 2, 3, and 4 in mouse and human serum. The prevalence of specific anti-VP2 IgG antibodies against HBoV1-4 was determined in different age groups of healthy individuals aged 0-70 years old in Beijing, China, using a competition ELISA assay based on virus-like particles of HBoV1-4. The seroprevalence of HBoV1-4 was 50%, 36.9%, 28.7%, and 0.8%, respectively, in children aged 0-14 years (n = 244); whereas the seroprevalence of HBoV1-4 was 66.9%, 49.3%, 38.7% and 1.4%, respectively, in healthy adults (≥ 15 years old; n = 142). The seropositive rate of HBoV1 was higher than that of HBoV2, HBoV3, and HBoV4 in individuals older than 0.5 years. Furthermore, IgG seroconversion of HBoV1 (10/31, 32.3%), HBoV2 (8/31, 25.8%), and HBoV3 (2/31, 6.5%) was found in paired sera collected from children with respiratory tract infections who were positive for HBoV1 according to PCR analysis. CONCLUSIONS/SIGNIFICANCE: Our data indicate that HBoV1 is more prevalent than HBoV2, HBoV3, and HBoV4 in the population we sampled in Beijing, China, suggesting that HBoV species may play differential roles in disease

Contribution of Microbe-Mediated Processes in Nitrogen Cycle to Attain Environmental Equilibrium

Nitrogen (N), the most important element, is required by all living organisms for the synthesis of complex organic molecules like amino acids, proteins, lipids etc. Nitrogen cycle is considered to be the most complex yet arguably important cycle next to carbon cycle. Nitrogen cycle includes oxic and anoxic reactions like organic N mineralization, ammonia assimilation, nitrification denitrification, anaerobic ammonium oxidation (anammox), dissimilatory nitrate reduction to ammonium (DNRA), comammox, codenitrification etc. Nitrogen cycling is one of the most crucial processes required for the recycling of essential chemical requirements on the planet. Soil microorganisms not only improve N-cycle balance but also pave the way for sustainable agricultural practices, leading to improved soil properties and crop productivity as most plants are opportunistic in the uptake of soluble or available forms of N from soil. Microbial N transformations are influenced by plants to improve their nutrition and vice versa. Diverse microorganisms, versatile metabolic activities, and varied biotic and abiotic conditions may result in the shift in the equilibrium state of different N-cycling processes. This chapter is an overview of the mechanisms and genes involved in the diverse microorganisms associated in the operation of nitrogen cycle and the roles of such microorganisms in different agroecosystems

Mn-based mixed oxides for low temperature NOx adsorber applications

Pd-promoted ternary oxides of the type Mn-Ce-Zr and Mn-Pr-Zr were characterized and evaluated for low temperature NOx storage applications such as diesel vehicle cold starts. While X-ray diffraction data were in all cases consistent with the formation of solid solutions, Mn/Zr and Mn/Ce(Pr) ratios found by XPS were consistently higher than the bulk values, indicative of an enrichment of Mn at the surface of the solids. Both sets of Pd-promoted mixed oxides showed remarkably high NOx storage efficiency in the range 80–160 °C, while a 1.8% Pd/Mn(27)-Ce(7)-Zr catalyst showed excellent NOx storage in simulated cold start experiments. Moreover, ramping the temperature to 370 °C in these experiments, simulating higher speed operation, resulted in near complete purging of stored NOx from the catalyst. NOx storage efficiency in isothermal storage experiments was found to improve with increasing Mn content for the 1%Pd/Mn(x)-Ce(7)-Zr series (x = 9, 18, 27 wt.%), DRIFTS measurements showing that relative to Ce-Zr mixed oxides, Mn incorporation favored NOx storage as nitrate. During temperature programmed desorption (TPD) two main desorption events were observed, corresponding to decomposition of nitrites (up to 200 °C), followed by loss of nitrates (⁓200–400 °C). Nitrates stored on Pd/Mn-Ce(Pr)-Zr mixed oxides desorbed during TPD at lower temperatures than for CeO2-ZrO2 mixed oxides, a finding attributed to the lower basicity of Mn compared to Ce. Hydrothermal aging of 1.8%Pd/Mn(27)-Ce(7)-Zr at 700 °C reduced NOx storage efficiency, although the catalyst was still able to store significant amounts of NOx. However, catalyst sulfation led to a large decrease in NOx storage efficiency and the efficiency could not be completely recovered with lean or rich desulfations at high temperatures.This project was funded by the National Science Foundation and the U.S. Department of Energy (DOE) under award no. CBET-1258742

CeO2-M2O3 Passive NOx Adsorbers for Cold Start Applications

Pt/CeO2-M2O3 and Pd/CeO2-M2O3 (M = La, Pr, Y, Sm, or Nd) were prepared by co-precipitation and impregnation and were investigated for potential passive NOx adsorber (PNA) use. During NOx storage at 120 °C, it was found that the amount of NOx stored as a function of time for Pt-promoted materials was higher than the Pd-promoted counterparts. For Pt/CeO2-M2O3 samples doped at the 5% level, NOx storage efficiency (NSE) followed the order Pr > Nd > Sm > Ce (undoped) > Y, La. Increasing dopant content from 5 to 20% decreased NSE in most cases, although in the case of Pr, NSE was increased. During subsequent NOx-temperature-programmed desorption (TPD), two NOx desorption events were apparent in all cases, the first occurring below 350 °C and the second occurring in the range 350–500 °C. Doping with Pr promoted the release of increased amounts of NOx below 350 °C compared to samples doped with other lanthanides; moreover, increasing the content of all doping metals except Pr shifted desorption peaks to higher temperatures, while the opposite trend was observed for Pr. Promotion with Pd was also examined, resulting in an increase of NOx desorption at low temperatures (<350 °C) relative to Pt. These results can be rationalized in terms of the ability of Pr to create vacancies in the CeO2 lattice, which facilitate NOx adsorption, and by the superior NO oxidation activity of Pt relative to Pd, which promotes NOx storage as nitrates possessing high thermal stability.This project was funded by the National Science Foundation and the US Department of Energy (DOE) under award no. CBET-1258742

Group 11 (Cu, Ag, Au) promotion of 15%Co/Al(2)O(3) Fischer-Tropsch synthesis catalysts

Co/Al(2)O(3) Fischer-Tropsch synthesis catalysts promoted with different quantities of Group 11 metals (Cu, Ag, Au) were characterized and tested. The presence of relatively small quantities of such metals enhanced Co reducibility and, in the cases of Ag and Au, improved the surface Co metal active site densities. EXAFS experiments with the most loaded catalyst samples show that only Co-Co and Me-Me (Me = Cu, Ag and Au) coordination could be observed. This suggests that the greater fraction of the metals form different phases. However, the reduction promoting effect of the Group 11 metal is severely hampered once the catalyst receives a mild passivation treatment following primary reduction. An explanation in terms of promoter segregation during primary reduction is proposed. At lower promoter levels (0.83%Ag and 1.51%Au) and higher Ag levels (2.76%), significant gains in Co active site densities were achieved resulting in improved CO conversion levels relative to the unpromoted catalyst. Moreover, slight decreases in light product (e.g., CH(4)) selectivity and slight increases in C(5)+ selectivity were achieved. At high Au loading (5.05%), however, too much Au was loaded which, although significantly increasing the fraction of Co reduced, blocked Co surface sites and resulted in decreased Co conversion rates. While Cu facilitated Co reduction, the increased fraction of reduced Co did not translate to improved active site densities. It appears that a fraction of Cu tended to cover the rim of Co clusters, resulting in decreases in CO conversion rates and detrimental increases in light product selectivity. (C) 2009 Elsevier B.V. All rights reserved.Center for Applied Energy ResearchCenter for Applied Energy ResearchCommonwealth of KentuckyCommonwealth of Kentuck

NOx storage-reduction characteristics of Ba-based lean NOx trap catalysts subjected to simulated road aging

In order to study the effect of washcoat composition on lean NOx trap (LNT) aging characteristics, fully formulated monolithic LNT catalysts containing varying amounts of La-stabilized CeO2 (5 wt% La2O3) or CeO2-ZrO2 (Ce:Zr = 70:30) were subjected to accelerated aging on a bench reactor. Subsequent catalyst evaluation revealed that aging resulted in deterioration of the NOx storage, NOx release and NOx reduction functions, whereas the observation of lean phase NO2 slip for all of the aged catalysts indicated that LNT performance was not limited by the kinetics of NO oxidation. After aging, all of the catalysts showed increased selectivity to NH3 in the temperature range 250–450 °C. TEM, H2 chemisorption, XPS and elemental analysis data revealed two main changes which can explain the degradation in LNT performance. First, residual sulfur in the catalysts, present as BaSO4, decreased catalyst NOx storage capacity. Second, sintering of the precious metals in the washcoat was observed, which can be expected to decrease the rate of NOx reduction. Additionally, sintering is hypothesized to result in segregation of the precious metal and Ba phases, resulting in less efficient NOx spillover from Pt to Ba during NOx adsorption, as well as decreased rates of reductant spillover from Pt to Ba and reverse NOx spillover during catalyst regeneration. Spectacular improvement in LNT durability was observed for catalysts containing CeO2 or CeO2-ZrO2 relative to their non-ceria containing analog. This was attributed to (i) the ability of ceria to participate in NOx storage/reduction as a supplement to the main Ba NOx storage component; (ii) the fact that Pt and CeO2(-ZrO2) are not subject to phase segregation; and (iii) the ability of ceria to trap sulfur, resulting in decreased sulfur accumulation on the Ba component

Effect of Pd promotion and catalyst support on the Ni-catalyzed deoxygenation of tristearin to fuel-like hydrocarbons

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