Coke Deposition and Structural Changes of Pellet V2O5/NaY-SiO2 in Air Regeneration: The Effects of Temperature on Regeneration

V2O5/NaY-SiO2 adsorbents were prepared by soaking up vanadium oxalate precursors into pellet NaY-SiO2. The NaY-SiO2 supports were prepared from NaY-SiO2 dough followed by extrusion and calcination at 450 °C. Ethanol was used as a model adsorbate to test the performance of the adsorbents. The regeneration efficacy, defined as the ratio of the adsorption capacity of a regenerated adsorbent to that of the fresh adsorbent, was investigated through the dynamics of fixed-bed adsorption (breakthrough curve). TPO, DSC, and FT-IR were used to characterize carbonaceous species on the adsorbents; meanwhile, synchrotron XRPD, XAS, and the N2 isotherm were used to characterize the zeolite, vanadia structure, and surface area, respectively. The results indicated that in low temperature (300 °C) regeneration, adsorption sites covered by alkylated aromatic coke formed during regeneration, causing adsorbent deactivation. In contrast, during regeneration at a high temperature (450 °C), the deactivation was caused by the destruction of the NaY framework concomitant with channel blockage, as suggested by the BET surface area combined with Rietvelt XRPD refinement results. In addition, the appearance of V-O-V contribution in the EXAFS spectra indicated the aggregation of isolated VO4, which led to a decrease in the combustion rate of the carbonaceous species deposited on the adsorbents. For regeneration at 350 and 400 °C, only trace coke formation and minor structural destruction were observed. Long-term life tests indicated that regeneration at 400 °C presents a higher maintenance of stability.

Source and Source Region of Carbonaceous Species and Trace Elements in PM10 over Delhi, India

This study investigated the carbonaceous species [elemental carbon (EC), organic carbon (OC), water soluble organic carbon (WSOC)] along with the trace elements (Al, S, Ti, Mn, Fe, Cu, Zn, As, Br, Pb, Cr, F, Cl, Na, K, Mg, Ca, P) in PM10 over the megacity Delhi, India (collected from 2015–2019) to address certain significant scientific issues (i.e., what are the directionality or pathway of these emissions; what are the possible emission sources which are distressing the observation site; what are the periodical variations in these emissions; and whether the emissions are local, regional, or trans-boundary). Integration of these problems are addressed using various statistical approaches including potential source areas (PSA) [using hybrid modelling i.e., potential source contribution factor (PSCF)], the conditional bivariate probability function (CBPF), and principal component analysis (PCA). Furthermore, seasonal PSCF and CBPF indicate both local source (highly polluted residential areas, traffic congestions, and industrial emissions) and regional sources (Haryana, Punjab) dominancy during winter and post-monsoon seasons at the receptor site, whereas during summer and monsoon along with local source and the regional, trans-boundaries (Indo-Gangatic plane, Pakistan, Afghanistan, and Bay of Bengal) air parcel patterns also contribute to the aerosol loading at the sites. Moreover, the PCA approach framed four common sources [crustal/road dust (RD), industrial emission (IE), fossil fuel combustion + biomass burning (FCC+ BB), vehicular emission (VE)] with one mixed source over the sampling site of Delhi.

Enhanced Methanol Oxidation Activity of PtRu/C100−xMWCNTsx (x = 0–100 wt.%) by Controlling the Composition of C-MWCNTs Support

PtRu nanoparticles decorated on carbon-based supports are of great interest for direct methanol fuel cells (DMFCs). In this study, PtRu alloy nanoparticles decorated on carbon Vulcan XC-72 (C), multi-walled carbon nanotubes (MWCNTs), and C-MWCNTs composite supports were synthesized by co-reduction method. As a result, PtRu nanoparticles obtained a small mean size (dmean = 1.8–3.8 nm) with a size distribution of 1–7 nm. We found that PtRu/C60MWCNTs40 possesses not only high methanol oxidation activity, but also excellent carbonaceous species tolerance ability, suggesting that C-MWCNTs composite support is better than either C or MWCNTs support. Furthermore, detailed investigation on PtRu/C100−xMWCNTsx (x = 10–50 wt.%) shows that the current density (Jf), catalyst tolerance ratio (Jf/Jr), and electron transfer resistance (Ret) are strongly affected by C-MWCNTs composition. The highest Jf is obtained for PtRu/C70MWCNTs30, which is considered as an optimal electrocatalyst. Meanwhile, both PtRu/C70MWCNTs30 and PtRu/C60MWCNTs40 exhibit a low Ret of 5.31–6.37 Ω·cm2. It is found that C-MWCNTs composite support is better than either C or MWCNTs support in terms of simultaneously achieving the enhanced methanol oxidation activity and good carbonaceous species tolerance.

Seasonal Variation and Sources of Carbonaceous Species and Elements in PM2.5 and PM10 Over the Eastern Himalaya

The study represents the seasonal characteristics (carbonaceous aerosols and elements) and contribution of prominent sources PM2.5 and PM10 in the high altitude of the eastern Himalaya (Darjeeling) during August 2018-July 2019. Carbonaceous aerosols [organic carbon (OC), elemental carbon (EC) and water soluble organic carbon (WSOC)] and elements (Al, Fe, Ti, Cu, Zn, Mn, Cr, Ni, Mo, Cl, P, S, K, Zr, Pb, Na, Mg, Ca, and B) in PM2.5 and PM10 were analyzed to estimate their possible sources. The annual average concentration of PM2.5 and PM10 were computed as 37±12 µg m-3 and 58±18 µg m-3, respectively. In the present case, total carbonaceous species in PM2.5 and PM10 were accounted for 20.6% of PM2.5 and 18.6% of PM10, respectively. Whereas, trace elements in PM2.5 and PM10 were estimated as 15% of PM2.5 and 12% of PM10, respectively. Monthly are seasonal variations in concentrations of carbonaceous aerosols and elements in PM2.5 and PM10 were also observed during the observational period. The positive relationship between OC & EC and OC & WSOC of PM2.5 and PM10 during all the seasons (except monsoon in case of PM10) indicate rheir common sources. The enrichment factors (EFs) and significant positive correlation of Al with othe crustal elements (Fe, Ca, Mg and Ti) of fine and coarse mode aerosols indicates the influence of mineral dust at the Darjeeling. Principal component analysis (PCA) resolved the four common sources (biomass burning + fossil fuel combustion (BB+FFC), crustal/soil dust, vehicular emissions (VE) and industrial emissions (IE)) of PM2.5 and PM10 in Darjeeling.