Temperature swing NO x adsorption-desorption cycles with gas mixtures consisting of 1000 ppm NO x , 5% O 2 , 3% H 2 O and N 2 were carried out on heteropolyacid adsorbents in the temperature range 80-170 C. Keggin type heteropolyacids having tungsten, molybdenum or their combination in octahedral coordination in combination with P, Si, Ge or B atoms in tetrahedral coordination were investigated. The heteropolyacids were used as pure compounds or supported on zeolite Y or the metal-organic framework Cu 3 (BTC) 2 (BTC represents 1,3,5-benzenetricarboxylic acid). The property of reversible adsorption of equimolar mixtures of NO and NO 2 was observed with Keggin type heteropolyacids based on W and combinations of W and Mo. Regeneration of the saturated adsorbent was achieved by cooling in a water vapor containing gas stream. The investigated heteropolyacids showed different water adsorption behavior. The capability of NO x adsorption was found to be related with crystal hydrate formation. Crystal water was much stronger retained in W-based compared to Mo-based Keggin compounds. Co-adsorption of NO and NO 2 molecules occurred only on Keggin compounds containing crystal water. The formation of H 2 NO 2 + compound out of NO, NO 2 and H 2 O in the interstitial spaces between Keggin units is proposed. The H-form and Co, Cu, Fe, Ni and Mn salts of Wells-Dawson type heteropolyacids were found to be readily dehydrated upon heating and did not show reversible NO x adsorption. Supported W-based Keggin heteropolyacid showed lower NO x adsorption capacity compared to the unsupported heteropolyacid.

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complexes · carbon monoxide · chromogenic detection · rhodium · sensors Carbonmonoxidegasisreferredtoas"silentkiller"because of its high toxicity and the inability of humans to detect it without using appropriate technology. CO detectors can be installed indoors and warn people about a dangerous CO concentration and thus protect them from this highly toxic inhalant. Carbon monoxide concentrations of 400 ppm are lethal within minutes, and the maximum CO exposure for adults is limited to 50 ppm over an eight hour period.Carbon monoxide sensing can be based either on semiconductor, electrochemical, chemical, or biomimetic principles. CO detectors are most often based on semiconducting metal oxides.[1] Upon exposure to molecular oxygen, negatively charged oxygen species (O 2 À or O À ) accumulate on the surface of, for example, SnO 2 , TiO 2 , or ZnO crystals, with formation of less conductive zones. CO gas, which can act as a reductant, reacts with the surface oxygen species to from CO 2 . As a consequence, the electrical conductance of the metal oxide film increases, thus triggering a response of the sensor.Semiconducting metal oxide sensors can be compounds that are pure or doped with different kinds of metals. Sensors based on constant potential amperometry (that is, current measurement when applying constant external voltage) and catalytic combustion are commercially available for the detection of CO.[2] Both types of sensors exploit the oxidation of carbon monoxide as a sensing principle. The first type operates by measuring the electrolytic current caused by oxidation of CO into CO 2 , while the second type measures the change of resistance in a Pt wire, where the change is caused by the heat released upon catalytic CO oxidation.Optochemical detectors containing a sensitive chemical compound that changes its optical properties upon reaction with the toxic molecule can be more simple and potentially cheaper than metal oxide sensors. The shortcomings of visual warning but especially the lack of sensitivity and selectivity of existing colorimetric probes in the critical concentration range presently reduce the quality of protection against CO poisoning.

Microporous silica and silica-alumina powders exhibit a reversible uptake and release of ammonia gas from water vapor containing gas mixtures at ambient temperature, with capacities of 0.9 and 2.0 mmol g-1 in the presence of 100 ppm and 1000 ppm NH3, respectively. The ammonia trapping mechanism was revealed using a combination of direct excitation 1H MAS, 1H-1H EXSY and 1H DQ-SQ NMR spectroscopy, indicating that the major part of the captured ammonia is blended in the hydrogen bonded water network in the pores of the adsorbent. A small fraction is irreversibly bound as result of protonation and chemisorption. While common ammonia adsorbents need thermal regeneration, microporous silica-alumina can be regenerated by sweeping with dry gas at ambient temperature, desorbing the physisorbed fraction together with occluded water. As carbon dioxide does not interfere with the ammonia absorption process, this reversible absorption process of ammonia gas at ambient temperature is particularly attractive for sensor applications.