After carbon, hydrogen, and oxygen, nitrogen is the next most abundant element in the human body. Inorganic and organic compounds of nitrogen feature prominently in many biological and environmental, as well as industrial, processes. In nature, the inorganic compounds of nitrogen are controlled by a reaction cycle called the nitrogen cycle (Figure 1).1 The denitrification pathway in this cycle, that is, the conversion of nitrate to dinitrogen, is employed by certain bacteria to produce ATP anaerobically and gain energy for cell growth. All organisms use ammonia as one of the starting building blocks for the synthesis of amino acids, nucleotides, and many other important biological compounds. Nitric oxide is * Corresponding author. E-mail: m.koper@chem.leidenuniv.nl. † Present address: Energy research Centre of The Netherlands (ECN), P.O. Box 1, 1755 ZG Petten, The Netherlands. ‡ Present address: Research, Development & Innovation, AkzoNobel Chemicals bv, Velperweg 76, P.O. Box 9300, 6800 SB Arnhem, The Netherlands. Chem. Rev. 2009, 109, 2209–2244 2209

Nitrogen cycle electrocatalysis.

Heterogeneous water phase catalysis as an environmental application: a review.

Membrane reactors applied to catalytic reactions are currently being studied in many places world-wide. Significant developments in membrane science and the vision of process intensification by multifunctional reactors have stimulated a lot of academic and industrial research, which is impressively demonstrated by more than 100 scientific papers on catalytic membrane reactors being published per year. Palladium as a noble metal with exceptional hydrogen permeation properties and, at the same time, broad applicability as a catalyst, first of all for hydrogenation, is part of many of these developments. This paper discusses two different membrane reactor concepts which both rely on supported palladium, on the one hand as a permselective membrane material, and on the other hand as base component of a membrane-type hydrogenation catalyst. Dense palladium composite membranes can be used for hydrogen separation from packed-bed catalysts in gas-phase hydrocarbon dehydrogenation reactions. Mesoporous membranes containing dispersed bimetallic Pd/X-clusters can be employed as so-called catalytic diffusers for liquid-phase hydrogenation, e.g. of nitrate and nitrite in water. The principles of both concepts are introduced, recently obtained experimental data are evaluated in connection with literature results, and the perspectives for further development are highlighted.

Membrane reactors for hydrogenation and dehydrogenation processes based on supported palladium

The paper reviews solid-catalyzed oxidation and reduction processes for the treatment of wastewater that contains small concentrations of toxic compounds and for which separation is not economical while biological treatment is not feasible. Specifically, the objectives are (1) to understand the interactions between catalytic materials and various pollutants, (2) to provide a database for catalyst selection, and (3) to assess the potential of these processes for commercialization. The review suggests the following well-investigated solutions:  (1) Supported metal (Ru/CeO2, Pt/CeO2, and Ru/C) and metal oxides (CuO−ZnO−CoO, MnO2/CeO2, CoO/Bi2O3, and V2O5/Al2O3) are the most promising catalysts for the destruction of refractory organic compounds with nearly 100% selectivity to CO2; (2) CoO/CeO2 and MnO2/CeO2 are the most active catalysts for ammonia oxidation at temperatures of 263−400 °C; (3) activated carbon, preferably in the presence of copper ions, is an active catalyst for the oxidation of cyanides and ...

Catalytic Abatement of Water Pollutants

Catalytic reduction of water contaminants using palladium (Pd)-based catalysts and hydrogen gas as a reductant has been extensively studied at the bench-scale, but due to technical challenges it has only been limitedly applied at the field-scale. To motivate research that can overcome these technical challenges, this review critically analyzes the published research in the area of Pd-based catalytic reduction of priority drinking water contaminants (i.e., halogenated organics, oxyanions, and nitrosamines), and identifies key research areas that should be addressed. Specifically, the review summarizes the state of knowledge related to (1) proposed reaction pathways for important classes of contaminants, (2) rates of contaminant reduction with different catalyst formulations, (3) long-term sustainability of catalyst activity with respect to natural water foulants and regeneration strategies, and (4) technology applications. Critical barriers hindering implementation of the technology are related to catalyst activity (for some contaminants), stability, fouling, and regeneration. New developments overcoming these limitations will be needed for more extensive field-scale application of this technology.

Critical Review of Pd-Based Catalytic Treatment of Priority Contaminants in Water

Development of catalysts for a selective nitrate and nitrite removal from drinking water

The invention concerns a method of removing substances present in water, in particular halogen-oxygen compounds which remain in the water as residues of disinfecting or are formed as by-products of oxidative water treatment. According to the invention, the substances present in water are removed by catalytic reduction in the presence of hydrogen on a supported precious metal catalyst.

Method of removing chlorine and halogen-oxygen compounds from water by catalytic reduction

In a method of introducing hydrogen into aqueous liquids without forming bubbles, the hydrogen is introduced through a composite membrane with, on the liquid side, a coating containing no pores. The preferred fields of application are biological or catalytic processes requiring the introduction of hydrogen to remove oxygen, nitrites or nitrates from aqueous solutions.

Method of introducing hydrogen into aqueous liquids without forming bubbles.

The description relates to an abrasion-resistant carrier catalyst for removing the nitrite and/or nitrate content of polluted water with selective nitrogen formation. The catalytically active metal component is palladium and/or rhodium or palladium and a metal from the copper group. The carrier consists of aluminum oxide in the "theta" and "kappa" modification and has either one maximum pore diameter in the 70 to 150 nm (700 to 1500 Å) range or two maxima in the 10 to 150 nm (100 to 1500 Å) range. The description also relates to a continuously operable process for the removal or reduction of the oxygen, nitrite and/or nitrate content of water by catalytic hydrogenation. The process is implemented using the novel carrier catalysts, the carriers being made of aluminum oxide of the theta and kappa modifications. Contamination of the catalyst is effectively prevented by the preferred use according to the fluidized bed process.

Abrasion-resistant carrier catalyst.

Process for the purification of aqueous peroxygen solutions comprising the treatment of an aqueous peroxygen solution with (a) at least one membrane purification step, (b) optionally at least one ion exchange purification step, (c) optionally at least one dilution step, and (d) at least one other purification step, all of which can be conducted in any sequence Aqueous peroxygen solutions having a TOC level of less than 1 mg/kg can be obtained by this process They can be used in the manufacture of semiconductors

Michael Sell

Papers

Development of catalysts for a selective nitrate and nitrite removal from drinking water

Method of removing chlorine and halogen-oxygen compounds from water by catalytic reduction

Method of introducing hydrogen into aqueous liquids without forming bubbles.

Abrasion-resistant carrier catalyst.

Process for the purification of aqueous peroxygen solutions, solutions obtainable thereby and their use