Formic Acid Dehydrogenation by a Cyclometalated κ3-CNN Ruthenium Complex

Hydrogen utilization as a sustainable energy vector is of growing interest. We report herein a cyclometalated ruthenium complex [Ru(κ3-CNN)(dppb)Cl], originally described by Baratta, to be active in the selective dehydrogenation (DH) of formic acid (FA) to H2 and CO2. TON's of more than 10000 were achieved under best conditions without observation of CO (detection limit 10 ppm). The distinguished behavior of the catalyst was explored varying the starting conditions. Our observation revealed the complex [Ru(κ3-CNN)(dppb)(OOCH)] as key species in the catalytic cycle. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA

Intermetallic nickel silicide nanocatalyst—A non-noble metal–based general hydrogenation catalyst

Hydrogenation reactions are essential processes in the chemical industry, giving access to a variety of valuable compounds including fine chemicals, agrochemicals, and pharmachemicals. On an industrial scale, hydrogenations are typically performed with precious metal catalysts or with base metal catalysts, such as Raney nickel, which requires special handling due to its pyrophoric nature. We report a stable and highly active intermetallic nickel silicide catalyst that can be used for hydrogenations of a wide range of unsaturated compounds. The catalyst is prepared via a straightforward procedure using SiO2 as the silicon atom source. The process involves thermal reduction of Si–O bonds in the presence of Ni nanoparticles at temperatures below 1000°C. The presence of silicon as a secondary component in the nickel metal lattice plays the key role in its properties and is of crucial importance for improved catalytic activity. This novel catalyst allows for efficient reduction of nitroarenes, carbonyls, nitriles, N-containing heterocycles, and unsaturated carbon–carbon bonds. Moreover, the reported catalyst can be used for oxidation reactions in the presence of molecular oxygen and is capable of promoting acceptorless dehydrogenation of unsaturated N-containing heterocycles, opening avenues for H2 storage in organic compounds. The generality of the nickel silicide catalyst is demonstrated in the hydrogenation of over a hundred of structurally diverse unsaturated compounds. The wide application scope and high catalytic activity of this novel catalyst make it a nice alternative to known general hydrogenation catalysts, such as Raney nickel and noble metal–based catalysts

Einflüsse von Minimalbodenbearbeitung und Transfermulch auf die perennierende Beikrautflora im Kartoffelbau

Reduced tillage enhances soil fertility and can help to avoid erosion. The drawback of increased weed pressure is a challenge for organic farmers due to the prohibition of herbicides. Mulch could be a way to suppress weeds and to introduce reduced tillage systems in potato cultivation. The number of perennial weeds were monitored in a comparison of two potato cultivation systems: conventional ploughing and hilling versus reduced tillage with dead mulch. In 2014, perennial weeds in the mulch system increased to double the number compared to the ploughed system. The reverse pattern was observed in 2015. This reversed effect was due to improved application methods of mulch with smaller particle size and a closer C/N-Ratio in the mulch in 2015 in combination with a severe spring drought in 2015 but not in 2014

Der Einfluss von reduzierter Bodenbearbeitung und Zwischenfrüchten auf die Unkrautsamenbank nach ökologischem Winterweizen- und Kartoffelbau

Conservation agriculture is one answer to counteract problems that are arising with climate change and soil degradation since the period of agricultural intensification. The main objectives of conservation agriculture are reduction of tillage intensity and a permanent soil cover by cash and cover crops. However, increased weed infestations are frequently reported in minimum tillage systems, particularly under organic management, resulting in increased weed seed banks. In two field experiments introduced in 2010 and 2011 and starting with two years grass-clover followed by winter wheat and potatoes, we evaluated the effect of chisel ploughing with mulch application to potatoes and different cover crops after winter wheat on the weed seed bank. Therefore, soil cores were taken before sowing wheat and after potato harvest and the viable weed seed bank from soil samples was assessed over a nine month period. Our results suggested a strong influence of weather conditions resulting in decreased and increased weed seed banks in the first and second experiments, respectively. Furthermore, winter wheat was confirmed as the main contributor of weed seeds to the seed bank resulting in dominances of winter annual weeds

Earth-abundant photocatalytic systems for the visible-light-driven reduction of CO2 to CO

Herein, we report a highly selective photocatalytic system, based on an in situ copper photosensitizer and an iron catalyst, for the reduction of CO2 to CO. Turnover numbers (TON) up to 487 (5 h) with selectivities up to 99% and ΦCO = 13.3% were observed. Stern-Volmer analysis allowed us to establish a reductive quenching mechanism between the Cu PS and electron donor

Immobilized Ru‐Pincer Complexes for Continuous Gas‐Phase Low‐Temperature Methanol Reforming‐Improving the Activity by a Second Ru‐Complex and Variation of Hydroxide Additives

Ru-pincer complexes were immobilized as supported liquid phase (SLP) materials to allow the methanol reforming reaction as continuous gas phase process. Under reaction conditions, the liquid phase forms from the hydroxide coating. Several hydroxides were screened and CsOH showed highest activity compared to the standard KOH coating. The well-known Ru-pincer complex carbonylchlorohydrido [bis(2-di-i-propylphosphinoethyl)amine]ruthenium(II) is limited in catalyzing the final step of the methanol reforming. Addition of a second complex, having a methylated backbone in the pincer-ligand, could overcome these limitations. Significant enhancement of the overall catalytic activity was observed

Mesoporous carbon nitride-silica composites by a combined sol-gel/thermal condensation approach and their application as photocatalysts

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Mesoporous carbon nitrides, silicas and their composites have been prepared by a combined sol–gel and thermal condensation approach. Precursors for the carbon nitride (cyanamide) and silica (TEOS) are mixed and condensed simultaneously. After condensation and heat treatment it is observed that the carbon nitride and silica formed highly interpenetrating mesophases which leads either to the formation of mesoporous carbon nitride or silica after selective removal of one of the phases. Importantly, the carbon nitride preserves its graphitic stacking even in the spatial confinement introduced by the surrounding silica phase. As both precursors are liquids this approach allows convenient shaping into thin and thick films or monoliths of mesoporous carbon nitrides. Enhanced photocatalytic activity is observed for the production of hydrogen from water when these mesoporous carbon nitrides are applied as photocatalyst in comparison to the bulk, but also to other mesoporous carbon nitrides, prepared by the reported two-step, hard templating approach.BMBF, 03IS2071D, Light2Hydroge

Der Einfluss von Minimalbodenbearbeitung, Zwischenfrüchten, Frischmulch und Kompostdüngung auf die Entwicklung der Kraut- und Knollenfäule

Reduced tillage combined with about 10cm of fresh mulch of a mixture of green peas and rye was compared to a system with conventional tillage with a plow for its effects on disease development of Phytophthora infestans. Within tillage treatments the precrops for potatoes were weedy fallow, vetch (Vicia sativa), or a mixture of oilseed radish and black oats with or without compost application. The Area Under the Disease Progress Curve in the minimum tillage and mulched plots was on average 881 while in the plowed plots it was 1336, a highly significant difference. Yield data are currently being analyzed and will be presented

Organic potatoes, reduced tillage and mulch in temperate climates

The experiments with mulching were done in a systems approach comparing potatoes as they are typically produced in Germany with ploughing to a system of non-inversion tillage combined with mulch. As the plots are integrated in two long-term experiments comparing ploughed versus minimum tillage it was not possible to integrate a mulched ploughed treatment or a non-mulched non-inversion tillage due to restrictions in plot size. We tested the effects of mulching in a ploughed system in 2015. There was no late blight but good erosion control (Pict.5) and yields were increased through mulching. Compost effects on the system were so far not clearly visible. It will most likely take several more years of regular applications to start seeing changes in system performance. Overall, mulching will change the potato system and it will depend very much on the local soil and climatic conditions if and when mulching will be positive (Table 1). On the one hand, mulching is labor intensive and requires the availability of materials to use. Besides freshly cut materials silage is an alternative option some farmers are using in vegetables in Germany. This reduces the dependence on the growing conditions for the mulch early in the season and likely also increases the fertilization effect. Farms that have no animals often mulch grass-clover. This will suppress N-fixation by the clover due to the nutrients in the mulch and thus reduce the usefulness of the grass-clover for nutrient accumulation. In addition it may result in leaching and thus loss of nutrients and even potentially harm the environment. Using the first and most rich harvest as mulch in the potatoes or alternatively making silage for later use is easier than composting such materials. Once the mulch is applied, no more mechanical weed control is done saving labor and energy. More importantly, it will also reduce the mechanical damage done to the potato foliage that makes them more susceptible to infections and it allows for profuse growth of fine roots into the applied mulch materials. Mulching also reduced Colorado potato beetles in both years to some extent but these data need confirmation. Also, the residual effects on the subsequent crop after the potatoes due to the increased input of organic amendments still need to be studied. Ecologically speaking mulching has many advantages. These advantages are especially important in water restricted areas. If and how mulching is feasible and economical depends on the specific conditions and organization of a farm, however

Two-photon, visible light water splitting at a molecular ruthenium complex

Water splitting to give molecular oxygen and hydrogen or the corresponding protons and electrons is a fundamental four-electron redox process, which forms the basis of photosynthesis and is a promising approach to convert solar into chemical energy. Artificial water splitting systems have struggled with orchestrating the kinetically complex absorption of four photons as well as the difficult utilization of visible light. Based on a detailed kinetic, spectroscopic and computational study of Milstein's ruthenium complex, we report a new mechanistic paradigm for water splitting, which requires only two photons and offers a new method to extend the range of usable wavelengths far into the visible region. We show that two-photon water splitting is enabled by absorption of the first, shorter wavelength photon, which produces an intermediate capable of absorbing the second, longer wavelength photon (up to 630 nm). The second absorption then causes O–O bond formation and liberation of O2. Theoretical modelling shows that two-photon water splitting can be used to achieve a maximum solar-to-hydrogen efficiency of 18.8%, which could be increased further to 28.6% through photochemical instead of thermal H2 release. It is therefore possible to exceed the maximum efficiency of dual absorber systems while only requiring a single catalyst. Due to the lower kinetic complexity, intrinsic utilization of a wide wavelength range and high-performance potential, we believe that this mechanism will inspire the development of a new class of water splitting systems that go beyond the reaction blueprint of photosynthesis