A model catalyst of the Pt/Ba/Al2O3 (PBA) type exhibited poor activity in NOx storage–reduction (NSR) at low temperatures (≤300 °C) even under a plasma-enhanced process. In order to achieve optimal NOx removal efficiency during plasma-assisted NOx storage–reduction in the presence of H2O and CO2, a PBA+LMF (LaMn0.9Fe0.1O3) catalyst was prepared by mechanical mixing. Compared to the PBA and LMF references, the combined PBA+LMF catalyst showed an obvious synergistic effect with respect to NOx storage capacity. With the assistance of H2 plasma in rich phase, higher NOx conversions could be obtained over the PBA+LMF sample over a wide temperature range (200–350 °C). The origin of the synergy was clarified on the basis of structure–activity correlations. The combination of non-thermal plasma and heterogeneous catalysis was proven to be very effective in improving the low temperature activity of lean NOx trap (LNT) catalysts.

•Doping redox active transition metal oxides into LNT catalysts improved NOx storage capacity.•Employing H2-plasma in rich phase assisted reduction of the stored NOx.•High NOx conversion can be obtained over a broad temperature range (150–350 °C).To improve the NOx storage capacity (NSC) of lean NOx trap (LNT) catalysts of the Pt/BaO/Al2O3 type, the catalyst was doped with redox active transition metals of Mn, Co, or Cu, respectively. Due to differences in the chemical states of the doped metals, the catalysts exhibited different catalytic behaviors. Co and Mn doped catalysts showed improved NO to NO2 oxidation ability, and therefore enhanced NOx storage capacities, which led to the increased cycle averaged NOx conversions as compared to a Pt/Ba/Al2O3 reference. However, being limited by NOx reduction in rich phase, the NOx conversions were still poor at low temperatures (<250 °C). By employing an H2-plasma in rich phase to assist NOx reduction, NOx conversions were greatly enhanced especially for low temperatures (⩽250 °C). The best properties were achieved over Pt/Co/Ba/Al2O3 catalyst which exhibited NOx conversions higher than 80% in the whole temperature range (150–350 °C) and best SO2 resistance abilities.Download high-res image (85KB)Download full-size image

•Physically mixed LMF with Ba/Al catalysts exhibit super NSC.•Pt functioned in H2 adsorption and dissociation in plasma-assisted rich phase•Pt on alumina gives the best regeneration ability in plasma-assisted rich phase.The storage and reduction of NOx was examined over a series of mechanically mixed LaMn0.9Fe0.1O3 (LMF) + Ba/Al2O3 (BA), Pt-LMF + BA and LMF + BA + Pt/Al2O3 (PA) catalysts in order to investigate the function of Pt in plasma-assisted NSR reaction. Efforts were also made to optimize the location of Pt to give the best H2 reduction ability.Download high-res image (142KB)Download full-size image

Lignin depolymerization represents a promising approach to the sustainable production of aromatic molecules. One potential approach to the stepwise depolymerization of lignin involves oxidation of the benzylic alcohol group in β-O-4 and β-1 linkages, followed by Baeyer–Villiger oxidation (BVO) of the resulting ketones and subsequent ester hydrolysis. Towards this goal, BVO reactions were performed on 2-adamantanone, a series of acetophenone derivatives, and lignin model compounds using a tin beta zeolite/hydrogen peroxide biphasic system. XRD, 119Sn MAS NMR spectroscopy, DRUVS and XPS were used to determine tin speciation in the catalyst, the presence of both framework Sn and extra framework SnO2 being inferred. Conversion of ketones to BVO products was affected by electron donation as well as steric hindrance, 4′-methoxyacetophenone affording the highest yield of ester (81%). As the size and complexity of the ketone increased, excess hydrogen peroxide was typically needed for successful BVO. Yields of ester products derived from β-O-4 and β-1 lignin models were modest due to the formation of polymeric material stemming from direct ring hydroxylation.

Pt- and Pd-promoted CexZr1–xO2 mixed oxides were characterized and investigated for passive NOx adsorber applications. X-ray diffraction analysis revealed a phase transition from tetragonal to cubic with increasing cerium content in CexZr1–xO2, while H2 and CO chemisorption data in all cases indicated average Pt and Pd particle sizes of close to 2 nm. H2-temperature programmed reduction (TPD) measurements revealed a shift of the Pt reduction peak to higher temperature with increasing Ce content, consistent with a corresponding increase in the degree of Pt oxidation. According to microreactor data, doping Ce into the ZrO2 lattice resulted in a significant improvement in low temperature (80–160 °C) NOx storage efficiency. Diffuse reflectance infrared Fourier transform spectroscopy measurements on Pt/CexZr1–xO2 showed that as Ce content increased, relatively more nitrite species were generated during NOx storage. However, oxidation of nitrite to nitrate during subsequent NOx-TPD—increasing the concentration of more thermally stable nitrate—also correlated with increased Ce content. The use of Pd as a promoter resulted in decreased NOx storage efficiency compared to Pt, although low-temperature NOx desorption behavior was improved. This is attributed to decreased formation of nitrate during NOx storage compared to that of Pt, as well as the lower activity of Pd for oxidation of nitrite to nitrate during subsequent NOx-TPD. To achieve more balanced NOx storage and desorption behavior, Ce0.2Zr0.8O2 was promoted with both Pt and Pd, resulting in superior overall NOx performance relative to its Pt and Pd analogues. After hydrothermal aging at 750 °C for 16 h, the copromoted sample still maintained excellent NOx adsorption–desorption performance.

A novel cyclic flow photobioreactor (PBR) for the capture and recycle of CO2 using microalgae was designed and deployed at a coal-fired power plant (Duke Energy’s East Bend Station). The PBR was operated continuously during the period May–September 2015, during which algae productivity of typically 0.1–0.2 g/(L day) was obtained. Maximum CO2 capture efficiency was achieved during peak sunlight hours, the largest recorded CO2 emission reduction corresponding to a value of 81 % (using a sparge time of 5 s/min). On average, CO2 capture efficiency during daylight hours was 44 %. The PBR at East Bend Station also served as a secondary scrubber for NOx and SOx, removing on average 41.5 % of the NOx and 100 % of the SOx from the flue gas. The effect of solar availability and self-shading on a rudimentary digital model of the cyclic flow PBR was examined using Autodesk Ecotect Analysis software. Initial results suggest that this is a promising tool for the optimization of PBR layout with respect to the utilization of available solar radiation.

CeO2 promoted with either 1 wt% Pt or 1 wt% Pd was evaluated as a model system for passive NOx adsorber applications. According to NOx storage experiments conducted over the temperature range 80–160 °C, promotion with Pt resulted in higher NOx storage efficiencies than for the Pd-promoted material. However, for NOx storage at 80 and 120 °C, the latter released more NOx below 350 °C during temperature-programmed desorption in relative and absolute terms, the Pt analog releasing most of its stored NOx above 350 °C. DRIFT spectra showed that the use of Pd leads to preferential adsorption of NOx in the form of nitrites, while predominately nitrate formation is observed over the Pt promoted material. Overall, the use of Pd promoted CeO2 is preferred for low temperature NOx storage and release due to its ability to store NOx as thermally labile nitrites.

The oxidation of alcohols to carbonyl compounds is an important reaction in synthetic organic chemistry. While stoichiometric oxidants are effective for this transformation, they often produce large amounts of toxic waste, which renders them unacceptable from an environmental and economic perspective. Consequently, there is a strong impetus to develop catalytic processes that utilize environmentally friendly, inexpensive primary oxidants, the use of molecular oxygen being particularly attractive. Recently, hydrotalcites have attracted attention as both catalysts and catalyst supports for the selective oxidation of alcohols to ketones and aldehydes, using either oxygen or TBHP as the oxidant. This review is intended to provide a comprehensive summary of work performed in this area to date. The effects of composition and structure on catalyst properties are highlighted, and mechanistic aspects are discussed.

Lignin oxidation reactions are increasingly being utilized in the field of lignin valorization. This is primarily due to the prospect of obtaining high-value aromatic products from cleavage of the Cα–Cβ bond in lignin's β-O-4 linkages. In this work activated dimethyl sulfoxide reactions, namely Swern and Parikh–Doering oxidations, were performed both on lignin and on compounds modeling the β-O-4 linkage. When phenolic moieties were present in the model compounds, enol ethers were formed rather than the ketone expected from oxidation of the β-O-4 alcohol moiety. Conversely, in the absence of phenolic moieties, the β-O-4 alcohol was oxidized to a ketone. These results are interpreted in terms of enol ether formation from a quinone methide intermediate formed via deprotonation of the phenolic –OH in the initial sulfur ylide species. When applied to Kraft lignin, alcohol oxidation was observed at both the α and γ positions in lignin under both Swern and Parikh–Doering conditions, although analytical data were unable to shed light on the relative importance of enol ether versus 1,3-diketone formation (or its tautomer). These results emphasize the importance of working with realistic lignin model compounds in order to understand and develop lignin chemistry.

This study focused on devising a method for accurately analyzing the reaction products derived from the upgrading of fats and oils to hydrocarbons. A single method capable of identifying and quantifying all the major constituents commonly found in samples of interest was developed, including the triglycerides and fatty acids constituting the feed, the alkanes resulting from the deoxygenation of the feed, and other intermediates and byproducts, such as alkenes, alcohols, aldehydes, and esters. A standard GC–FID-based method for the analysis of hydrocarbon mixtures (ASTM D 2887) was used as a starting point, and through a number of modifications to both hardware and programming, a method capable of affording a single chromatogram in which all the aforementioned components are fully eluted and well-resolved was developed. In addition to its reliability and its versatility, this approach is relatively fast, straightforward, and inexpensive, as no sample derivatization prior to analysis is required.

CO2 capture and recycle using microalgae was demonstrated at a coal-fired power plant (Duke Energy’s East Bend Station, Kentucky). Using an in-house designed closed loop, vertical tube photobioreactor, Scenedesmus acutus was cultured using flue gas as the CO2 source. Algae productivity of 39 g/(m2 day) in June–July was achieved at significant scale (18,000 L), while average daily productivity slightly in excess of 10 g/(m2 day) was demonstrated in the month of December. A protocol for low-cost algae harvesting and dewatering was developed, and the conversion of algal lipids—extracted from the harvested biomass—to diesel-range hydrocarbons via catalytic deoxygenation was demonstrated. Assuming an amortization period of 10 years, calculations suggest that the current cost of capturing and recycling CO2 using this approach will fall close to $1,600/ton CO2, the main expense corresponding to the capital cost of the photobioreactor system and the associated installation cost. From this it follows that future cost reduction measures should focus on the design of a culturing system which is less expensive to build and install. In even the most optimistic scenario, the cost of algae-based CO2 capture is unlikely to fall below $225/ton, corresponding to a production cost of ~$400/ton biomass. Hence, the value of the algal biomass produced will be critical in determining the overall economics of CO2 capture and recycle.

Herein we report the fast pyrolysis of the lignin monomers sinapyl and coniferyl alcohol, as well as mixtures of the two, at 650 °C using pyrolysis–GC/MS. The total ion chromatogram area % of certain marker pyrolysates for each alcohol were summed and used to calculate sinapyl:guaiacyl (S:G) ratios in the mixtures; these ratios were then plotted against the actual molar S:G ratios of the starting material. 13 coniferyl alcohol marker pyrolysates and 9 sinapyl alcohol marker pyrolysates provided acceptable linear correlation, whereas several other marker groups chosen did not correlate to the actual S:G ratio in the starting material. Results indicated that the demethoxylation of sinapyl alcohol and/or its pyrolysates occurs during pyrolysis at 650 °C; however, the amount of demethoxylated products generated is statistically insignificant. Having obtained the pyrolysis profile of the various S:G mixtures, marker pyrolysates for the calculation of the S:G ratio in lignin can be carefully selected according to unique samples. These marker groups can then be calibrated against known S:G ratios to provide analysis of the actual S:G ratio of lignin in biomass. For example, pyrolysates chosen from the pyrolysis of peach pit lignin were calibrated in order to determine the S:G ratio in peach pit lignin. The resulting S:G ratio was similar to that obtained from capillary electrophoresis of the products from KMnO4 oxidation of the peach pit lignin.Highlights► We studied sinapyl and coniferyl alcohol and their mixtures using pyrolysis–GC/MS. ► Sum area percent ratios of pyrolysates from each alcohol were calculated. ► Linear correlations existed between sum area percent S:G ratios and molar S:G ratios. ► The S:G ratio of lignin was measured via pyrolysis–GC/MS. ► Pyrolysis–GC/MS S:G ratios agreed with capillary electrophoresis of oxidized lignin.

N2O formation and consumption were investigated over a coupled LNT–SCR system consisting of a low-precious metal loaded Pt/Rh LNT catalyst and a commercial Cu–zeolite SCR catalyst. Under lean–rich cycling conditions, N2O emissions from the LNT were found to be partially mitigated by the downstream SCR catalyst. N2O decomposition over the SCR catalyst was observed in the absence of reductant immediately after the switch to rich conditions, while N2O reduction occurred after subsequent breakthrough of the reductant from the LNT. Steady-state data indicate that the former process is weakly promoted by NO which breaks through the LNT at the same time as the N2O. Steady-state experiments revealed the order H2 > NH3 > CO > C3H6 for the efficacy of N2O reduction with different reductants. These findings suggest that coupled LNT–SCR systems can not only improve overall NOx conversion levels but can also mitigate N2O emissions from the LNT catalyst under actual driving conditions.

The selective catalytic reduction of NOx with hydrocarbons (HC-SCR) on functionalized multiwalled carbon nanotube (fMWCNT)-supported metal catalysts was investigated using a transient technique, together with kinetic and adsorption measurements. Results from the transient studies provide an explanation for the characteristic volcano shape of the NOx conversion curves: below Tmax, the temperature of maximum NOx conversion, the catalyst surface is covered by hydrocarbonaceous species, which results in the suppression of NOx reduction activity. Above Tmax, O2 adsorption becomes prevalent, favoring oxidation of both NO and the hydrocarbon. In an effort to understand the origin of the superior NOx reduction activity shown by 3:1 Pt–Rh/fMWCNTs as compared to Pt/fMWCNTs, Temperature Programmed Desorption (TPD) measurements were undertaken. Results indicate that hydrocarbon and/or hydrocarbon-derived species are more strongly adsorbed on the alloy than on Pt alone, while NO adsorption is weaker on the alloy than on Pt. This is suggested to give rise to a higher concentration of partially oxidized hydrocarbon intermediates on the surface of the Pt–Rh catalyst at the temperature of maximum deNOx activity, leading to higher NOx reduction activity.

A model catalyst of the Pt/Ba/Al2O3 (PBA) type exhibited poor activity in NOx storage–reduction (NSR) at low temperatures (≤300 °C) even under a plasma-enhanced process. In order to achieve optimal NOx removal efficiency during plasma-assisted NOx storage–reduction in the presence of H2O and CO2, a PBA+LMF (LaMn0.9Fe0.1O3) catalyst was prepared by mechanical mixing. Compared to the PBA and LMF references, the combined PBA+LMF catalyst showed an obvious synergistic effect with respect to NOx storage capacity. With the assistance of H2 plasma in rich phase, higher NOx conversions could be obtained over the PBA+LMF sample over a wide temperature range (200–350 °C). The origin of the synergy was clarified on the basis of structure–activity correlations. The combination of non-thermal plasma and heterogeneous catalysis was proven to be very effective in improving the low temperature activity of lean NOx trap (LNT) catalysts.