Restructuring of titanium oxide overlayers over nickel nanoparticles during catalysis.

Reducible supports can affect the performance of metal catalysts by the formation of suboxide overlayers upon reduction, a process referred to as the strong metal-support interaction (SMSI). A combination of operando electron microscopy and vibrational spectroscopy revealed that thin TiOx overlayers formed on nickel/titanium dioxide catalysts during 400°C reduction were completely removed under carbon dioxide hydrogenation conditions. Conversely, after 600°C reduction, exposure to carbon dioxide hydrogenation reaction conditions led to only partial reexposure of nickel, forming interfacial sites in contact with TiOx and favoring carbon-carbon coupling by providing a carbon species reservoir. Our findings challenge the conventional understanding of SMSIs and call for more-detailed operando investigations of nanocatalysts at the single-particle level to revisit static models of structure-activity relationships.

Improving the accuracy of nitrous oxide emission factors estimated for hotspots within dairy-grazed farms.

Nitrous oxide (N2O) emissions from dairy-grazing pastures can be dominated by large emissions from small areas ('hotspots') frequently used by grazing dairy cattle (i.e., water troughs and gateways). N2O emissions from these hotspots are quantified by investigating whether N2O emissions and emission factors (% of applied N emitted as N2O, EF3) from potential hotspots are different from non-hotspots. To better characterise N2O emissions from hotspots and non-hotspots of farms to understand their contributions to national agricultural greenhouse gas inventory calculations, a series of measurements were conducted during winter and spring on two NZ typical dairy farms with contrasting soil drainage (poorly versus well drained). Before measurements were taken, the soils either received a cow urine application or remained untreated. The results showed that changes in water-filled pore space (WFPS) and mineral N around water troughs and gateways, due to additional stock movements and disproportionate excreta-N deposition during previous grazing events, affected both background and total N2O emissions. But there was little impact on EF3 values (calculated using IPCC guidelines) from deposited urine between hotspot and pasture areas. These results suggest the same EF3 values can be used for both to calculate emissions from urine deposited on grazed pastures. However, these results raise concerns about higher background emission in hotspots subtracted from measured emissions from urine-N deposition in calculating EF3 values and discounting the effects of disproportionate N inputs in intensive agriculture on increased background emissions (legacy effect). This IPCC inventory method does not account for the legacy effect of N loading prior to the measurements which may underestimate the emissions. Thus, an allowance for higher hotspot background emissions could be included in the Inventory to accurately estimate total emissions from agriculture.

Use of a urease inhibitor to mitigate ammonia emissions from urine patches.

Urine deposition by grazing livestock is the single largest source of ammonia (NH3) volatilisation losses in New Zealand. Urease inhibitors (UI) have been used to mitigate NH3 losses from fertiliser urea and animal urine. In previous trials, the UI effect in reducing NH3 emissions from urine has been measured by applying urine mixed with the UI to the pasture soil thus increasing the chances of better interaction of the UI in inhibiting the urease enzyme. However, these trials do not represent a realistic grazing scenario where only urine is deposited onto the soil. This current research aimed to identify the best time to spray nBTPT (a UI containing 0.025% N-(n-butyl) thiophosphoric triamide) onto pasture soil to reduce NH3 losses from urine patches. The treatments were: a control (without urine and nBTPT), urine alone at 530 kg N ha-1 and urine plus nBTPT. The UI was applied to the chambers and soil plots 5 and 3 days prior to urine deposition, on the same day and 1, 3 and 5 after urine deposition in autumn. Ammonia losses were measured using the dynamic chamber method. The application of the inhibitor prior to urine deposition reduced NH3 losses with reductions of 27.6% and 17.5% achieved for UAgr-5 and UAgr-3, respectively. However, reductions in NH3 emission were 0.6-2.9% for inhibitor applied post urine deposition. There was also a reduction in both soil NH4 +-N concentration and soil pH in comparison with urine alone or with the treatments where nBTPT was applied after urine deposition.

Understanding carbon dioxide activation and carbon-carbon coupling over nickel.

Carbon dioxide is a desired feedstock for platform molecules, such as carbon monoxide or higher hydrocarbons, from which we will be able to make many different useful, value-added chemicals. Its catalytic hydrogenation over abundant metals requires the amalgamation of theoretical knowledge with materials design. Here we leverage a theoretical understanding of structure sensitivity, along with a library of different supports, to tune the selectivity of methanation in the Power-to-Gas concept over nickel. For example, we show that carbon dioxide hydrogenation over nickel can and does form propane, and that activity and selectivity can be tuned by supporting different nickel particle sizes on various oxides. This theoretical and experimental toolbox is not only useful for the highly selective production of methane, but also provides new insights for carbon dioxide activation and subsequent carbon-carbon coupling towards value-added products thereby reducing the deleterious effects of this environmentally harmful molecule.

Removing Hydrogen Sulfide Contamination in Biogas Produced from Animal Wastes.

Hydrogen sulfide (HS) contamination in biogas produced from animal wastes limits its use to cooking and precludes it from being used for heating, lighting, or electricity generation. This limitation results in the release to the atmosphere of between 3 and 51% of total biogas produced. Biogas contains 50 to 70% methane (CH), a potent greenhouse gas that contributes to global warming. This study aimed to develop a cost-effective HS filtering system using local materials rich in iron as iron oxide (FeO), which reacts readily with HS and forms adsorbed iron sulfide (FeS) when gas is passed through it. Here we tested the performance of seven New Zealand soils and sand, each at five different gas flow rates (59, 74, 94, 129, and 189 mL min). We found that three materials (allophanic soil, brown soil, and black sand) had stable HS removal efficiencies close to 100% at all gas flow rates, followed by typic sand (89-99%), raw sand (76-99%), acidic sand (48-89%), and podzol soil (58-87%). These results show that inexpensive and simple filters to remove HS from biogas can be made using local soils. Used soil in the filters can then be easily regenerated by exposure to the atmosphere and reused to achieve sustained HS removal efficiency.

Assessing the Performance of Floating Biofilters for Oxidation of Methane from Dairy Effluent Ponds.

Mitigating methane (CH) emissions from New Zealand dairy effluent ponds using volcanic pumice soil biofilters has been found to be a promising technology. Because the soil column biofilter prototype previously used was cumbersome, here we assess the effectiveness of volcanic pumice soil-perlite biofilter media in a floating system to remove high concentrations of CH emitted from a dairy effluent pond and simultaneously in a laboratory setting. We measured the CH removal over a period of 11 mo and determined methanotroph population dynamics using molecular techniques to understand the role of methanotroph population abundance and diversity in CH removal. Irrespective of the season, the pond-floating biofilters removed 66.7 ± 5.7% CH throughout the study period and removed up to 101.5 g CH m h. By contrast, the laboratory-based floating biofilters experienced more biological disturbances, with both low (∼34%) and high (∼99%) CH removal phases during the study period and an average of 58% of the CH oxidized. These disturbances could be attributed to the measured lower abundance of type II methanotroph population compared with the pond biofilters. Despite the acidity of the pond biofilters increasing significantly by the end of the study period, the biofilter encouraged the growth of both type I ( and ) and type II ( and ) methanotrophs. This study demonstrated the potential of the floating biofilters to mitigate dairy effluent ponds emissions efficiently and indicated methanotroph abundance as a key factor controlling CH oxidation in the biofilter.

First example of high loaded polymer-stabilized nanoclusters immobilized on hydrotalcite: effects in alkyne hydrogenation.

Poly(N-vinyl-2-pyrrolidone)-stabilized Pd-nanoclusters, for the first time exclusively supported on the hydrotalcite lateral surface, showed a remarkable catalytic performance in the selective hydrogenation of 3-hexyn-1-ol, which can be ascribed to both the influence of the protecting polymer PVP as well as the nature of the support.