Lean NOx reduction with methanol over supported silver catalysts

The oxygen rich and relatively cold exhaust gases from fuel-efficient combustion engines bring challenges for the reductive aftertreatment of NOx. In this context selective catalytic reduction over silver/alumina has shown positive results, especially with oxygenated reducing agents. In the present work, methanol, which is considered a promising renewable fuel, is evaluated as reducing agent for NOx over supported silver catalysts. The aim is to gain increased understanding of the catalytic processes, especially focusing on low-temperature activity and selectivity. The role of the supported silver species is studied, together with the influence of the support material and the gas composition, including the formation of hydrogen. For this purpose model catalysts were prepared, characterized and evaluated in flow-reactor experiments. The results show that the low-temperature activity for lean NOx reduction with methanol over silver/alumina is highly dependent on the composition of supported silver species and their interplay with adsorbed and gas phase species. This work provides new insights in the role of small silver species for the selectivity to N2 and the importance of somewhat larger silver species for catalytic activity at low temperature. These results were achieved by comparing silver/alumina samples of similar silver loading, but with different composition of silver species, as revealed by UV-vis spectroscopy, TEM and H2-TPR. Furthermore, comparisons of different support materials during methanol-SCR conditions, show a higher NOx reduction for silver supported on alumina than on ZSM-5. The NOx reduction over the alumina based catalyst is found to improve when the C/N ratio is moderately increased. The influence of the silver loading was studied and the results show that sol-gel silver/alumina with 3 wt% silver gives a high NOx reduction with methanol in a broad temperature interval, relevant for lean exhaust gases. Moreover, the observed formation of H2 from methanol gives an indication of that the high low-temperature activity associated with oxygenated reducing agents may be connected to the abstraction of hydrogen from the oxygenate, studied here for methanol by DRIFT spectroscopy. One effect of hydrogen, observed in the present work by UV-vis spectroscopy, is reduction of silver species

Exome Sequencing Reveals a Phenotype Modifying Variant inZNF528in Primary Osteoporosis With aCOL1A2Deletion

We studied a family with severe primary osteoporosis carrying a heterozygous p.Arg8Phefs*14 deletion in COL1A2, leading to haploinsufficiency. Three affected individuals carried the mutation and presented nearly identical spinal fractures but lacked other typical features of either osteogenesis imperfecta or Ehlers-Danlos syndrome. Although mutations leading to haploinsufficiency in COL1A2 are rare, mutations in COL1A1 that lead to less protein typically result in a milder phenotype. We hypothesized that other genetic factors may contribute to the severe phenotype in this family. We performed whole-exome sequencing in five family members and identified in all three affected individuals a rare nonsense variant (c.1282C > T/p.Arg428*, rs150257846) in ZNF528. We studied the effect of the variant using qPCR and Western blot and its subcellular localization with immunofluorescence. Our results indicate production of a truncated ZNF528 protein that locates in the cell nucleus as per the wild-type protein. ChIP and RNA sequencing analyses on ZNF528 and ZNF528-c.1282C > T indicated that ZNF528 binding sites are linked to pathways and genes regulating bone morphology. Compared with the wild type, ZNF528-c.1282C > T showed a global shift in genomic binding profile and pathway enrichment, possibly contributing to the pathophysiology of primary osteoporosis. We identified five putative target genes for ZNF528 and showed that the expression of these genes is altered in patient cells. In conclusion, the variant leads to expression of truncated ZNF528 and a global change of its genomic occupancy, which in turn may lead to altered expression of target genes. ZNF528 is a novel candidate gene for bone disorders and may function as a transcriptional regulator in pathways affecting bone morphology and contribute to the phenotype of primary osteoporosis in this family together with the COL1A2 deletion. (c) 2020 The Authors.Journal of Bone and Mineral Researchpublished by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).Peer reviewe

Effect of silver loading on the lean NOx reduction with methanol over Ag-Al2O3

The influence of silver loading on the lean NO x reduction activity using methanol as reductant has been studied for alumina supported silver catalysts. In general, increasing the silver loading (0-3 wt%), in Ag-Al 2 O 3 , shifts or extends the activity window, for lean NO x reduction towards lower temperatures. In particular Ag-Al 2 O 3 with 3 wt% silver is active for NO x reduction under methanol-SCR conditions in a broad temperature interval (200-500 C), with high activity in the low temperature range (maximum around 300 C) typical for exhaust gases from diesel and other lean burn engines. Furthermore, increasing the C/N molar ratio enhances the reduction of NO x . However, too high C/N ratios results in poor selectivity to N 2 . \ua9 2013 Springer Science+Business Media New York

Methanol Assisted Lean NOx Reduction Over Ag-Al2O3-Influence of Hydrogen and Silver Loading

The influence of hydrogen and silver loading on lean NOx reduction with methanol over Ag-Al2O3 are investigated by flow-reactor experiments, H-2-TPR, TEM and XPS. Reduction of silver at low temperatures over Ag-Al2O3 with high silver loading, suggests involvement of silver species/particles that are large (which is supported by the TEM analysis) and/or loosely bound to the support. The silver species reduced by hydrogen cannot be directly associated with the activity for NOx reduction under methanol-SCR conditions. Furthermore, the activity for NOx reduction increases slightly at low temperatures when hydrogen is added to the feed. However, also without co-fed hydrogen, a high low-temperature activity is achieved for methanol assisted lean NOx reduction over Ag-Al2O3

Role of hydrogen formation and silver phase for methanol-SCR over silver/alumina

Formation of reaction products over silver/alumina during lean NOx reduction with methanol was studied, with and without addition of hydrogen to the feed. The silver phase in silver/alumina was analyzed by UV–vis spectroscopy in order to elucidate the influence of silver loading and different gas environments. Formation of molecular hydrogen and reduction of supported silver species were observed during selective catalytic reduction (SCR) with methanol, without hydrogen in the feed. This availability of hydrogen and the reduction of silver are suggested to contribute to the high low-temperature activity connected to oxygenates (like alcohols) as reducing agents for NOx

Silver/alumina for methanol-assisted lean NOx reduction - on the influence of silver species and hydrogen formation

High low-temperature activity for lean NOx reduction can be achieved for silver/alumina by using an oxygenated reducing agent. In this system the catalytic reactions, including the H2 formation previously observed during methanol-SCR conditions, are strongly dependent on the composition of surface silver species. With the aim to increase the understanding of the role of supported silver species in combination with the methanol-SCR reactions, catalysts with the same silver loading but different composition of silver species are prepared by utilizing different preparation methods. The supported silver species are characterized by UV-vis spectroscopy and transmission electron microscopy, while the catalytic performance for lean NOx reduction with methanol is investigated in flow reactor experiments and surface species studied by DRIFT spectroscopy. The results indicate that hydrogen atoms are abstracted mainly from the methyl group during the conversion of surface species formed from methanol. The hydrogen atoms could contribute to reduction of the catalyst or affect the catalytic reactions in other ways, before they react to form H2 or H2O. Here, more H2O is formed over the samples containing more silver nanoparticles. The released hydrogen atoms are suggested to explain the high NOx reduction at low temperature associated with oxygenated reducing agents, rather than the subsequently formed gaseous H2. Furthermore, the results show that lean NOx reduction with methanol is determined by silver species in the size range from small silver clusters to small silver nanoparticles (<ca 20 nm). Small silver nanoparticles (<ca 20 nm) are concluded to catalyse formation of N2O. The role of silver ions and small clusters, on the other hand, is suggested to be promotion of N2 formation. The largest silver nanoparticles observed in this study (>ca 20 nm), however, do not have a significant impact on the catalytic reactions. Finally, in order to achieve both high low-temperature activity, as well as high selectivity to N2 a combination of small and somewhat larger silver species are needed