Portable device for generation of ultra-pure water vapor feeds

Abstract

A portable device for the generation of co-feeds of water vapor has been designed, constructed, and evaluated for flexible use as an add-on component to laboratory chemical reactors. The vapor is formed by catalytic oxidation of hydrogen, which benefits the formation of well-controlled minute concentrations of ultra-pure water. Analysis of the effluent stream by on-line mass spectrometry and Fourier transform infrared spectroscopy confirms that water vapor can be, with high precision, generated both rapidly and steadily over extended periods in the range of 100 ppm to 3 vol. % (limited by safety considerations) using a total flow of 100 to 1500 ml/min at normal temperature and pressure. Further, the device has been used complementary to a commercial water evaporator and mixing system to span water concentrations up to 12 vol. %. Finally, an operando diffuse reflective infrared Fourier transform spectroscopic measurement of palladium catalysed methane oxidation in the absence and presence of up to 1.0 vol. % water has been carried out to demonstrate the applicability of the device for co-feeding well-controlled low concentrations of water vapor to a common type of spectroscopic experiment. The possibilities of creating isotopically labeled water vapor as well as using tracer gases for dynamic experiments are discussed.

Water Inhibition in Methane Oxidation over Alumina Supported Palladium Catalysts

“…A reference spectrum merged from the average of 128 scans with a resolution of 2 cm –1 was recorded, and thereafter, a difference spectrum was measured to check spectral stability. Then 0.2 vol % CH 4 was added to the feed for dry CH 4 oxidation during 20 min followed by the addition of 1.0 vol % H 2 O using a water vapor generator described elsewhere, for another 40 min of wet CH 4 oxidation. Finally, CH 4 and H 2 O were removed from the feed for 20 min of oxidative treatment.…”

“…A reference spectrum merged from the average of 128 scans with a resolution of 2 cm −1 was recorded, and thereafter, a difference spectrum was measured to check spectral stability. Then 0.2 vol % CH 4 was added to the feed for dry CH 4 oxidation during 20 min followed by the addition of 1.0 vol % H 2 O using a water vapor generator described elsewhere, 59 for another 40 operando with a spectral resolution of 2 cm −1 , using a merged average of 64 scans for each spectrum recorded every 150 s. The second experimental procedure was carried out with the Pd/γ-Al 2 O 3 -500 sample only. An initial reference spectrum merged from the average of 32 scans with a resolution of 4 cm −1 was recorded in 2.0 vol % O 2 at the reaction temperature.…”

Hampered PdO Redox Dynamics by Water Suppresses Lean Methane Oxidation over Realistic Palladium Catalysts

“…Rather we show that for all these catalysts, water addition is of major importance and the behaviour of each catalyst can be judged on its own through the systematic use of the following gas composition sequences. [45] the redox dynamics of the particles could be followed in operando. In Figure 3, the variations in CH 4 -TOF and Pd K-edge white-line intensity (WLI) are shown for all catalysts under the mentioned perturbed conditions at 360°C.…”

Total oxidation of methane over Pd/Al2O3 at pressures from 1 to 10 atm

“…The flow reactor is a modified version of a portable water generation reactor. 37 The coated monolithic sample was fixed with quartz wool in a stainless steel tube (ID = 15 mm, L = 480 mm). The steel tube is heated by an electrical heating coil which is fixed directly upstream of the coated monolith sample to ensure a constant gas feed and reaction temperature.…”