Specific Interaction of PdO_x- and RuO_y-Modified Tin Dioxide with CO and NH₃ Gases: Kelvin Probe and DRIFT Studies

Abstract

The processes of selective interactions of gas sensitive nanocrystalline tin dioxide modified by catalytic PdO x and RuO y clusters with ppm-range concentrations of CO and NH 3 in air was studied.From simultaneous in situ work function and resistance measurements it was deduced that the modifiers promote specific interaction of gas molecules with the materials surface. In situ DRIFT studies revealed a key role of catalytic clusters in the selective gas-solid interactions. Specific CO chemisorption on Pd-sites was observed at room temperature. It is assumed to facilitate further oxidation of the molecules on the surface of SnO 2 /PdO x providing its low-temperature sensitivity to carbon monoxide. The selectivity of SnO 2 /RuO y to ammonia is due to the modifier-catalyzed deep oxidation of NH 3 molecules, which was evidenced by the evolvement of Ru-bound nitrosyl species during the interaction at raised temperature. The possible routes were suggested for specific SnO 2 /PdO x -CO and SnO 2 /RuO y -NH 3 interactions as a summary of experimental observations.

Understanding the Role of SnO2 Support in Water‐Tolerant Methane Combustion: In situ Observation of Pd(OH)2 and Comparison with Pd/Al2O3

“…In H 2 sensing, in the presence of O 2 , water formation occurs as expected, while at anaerobic conditions, hydrogen reacts with the metal oxide surface to create “rooted” hydroxyl groups and there is no detected desorbed water formation . In Pd/SnO 2 systems, CO activated on PdO x reacts with hydroxyls on SnO 2 surface with CO 2 formation . CH x reaction intermediates on Pt‐group active sites can be oxidized by OH ads on adjacent oxophilic Sn surface …”

“…[14] Our selective attention to Pd/SnO 2 was also fuelled by the fact that SnO 2 is used as sensors for CO and (less frequently) CH 4 or H 2 detection via catalytic oxidation mechanisms. [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] The humidity effect has been known in that field since 1970's [16][17][18][24][25][26][27][28][29][30][31][32] as it influences the sensor signal by electron generation: H 2 O + Sn lattice + O lattice $ (HOÀ Sn lattice ) + (O lattice H) + + e À . [19] SnO x surface has a high affinity to water that competes with CO adsorption; [27] the concentration of hydroxyl groups increases in the presence of gas-phase water and O 2 .…”

“…[21] In Pd/SnO 2 systems, CO activated on PdO x reacts with hydroxyls on SnO 2 surface with CO 2 formation. [23] CH x reaction intermediates on Ptgroup active sites can be oxidized by OH ads on adjacent oxophilic Sn surface. [33] In this work we follow the Pd speciation by X-ray absorption spectroscopy (XAS) of Pd/Al 2 O 3 and Pd/SnO 2 catalysts during methane combustion in the wet feed to observe the presence of Pd(OH) 2 hydroxyl species on Pd/PdO particles and to under-stand better the influence of the support on the water tolerance.…”

Organic-Inorganic Hybrid Materials for Room Temperature Light-Activated Sub-ppm NO Detection

“…(11) It is known that ruthenium compounds are active catalysts for the oxidation of nitrogen compounds [71][72][73][74]. This catalytic effect was also noted in the detection of nitrogen containing gases by SnO 2 based gas sensitive materials [75,76]. At the same time, the sensitivity of n-type semiconductor oxides to NO 2 significantly exceeds their sensitivity to NO [23].…”

Effects of Ag Additive in Low Temperature CO Detection with In2O3 Based Gas Sensors

“…The maximum at about 3400 cm −1 of the absorption band ascribed to hydroxyl groups is evidence for a predominance of rooted hydroxyls associated via hydrogen bonds (OH…..OH) [ 49 ]. FTIR investigations and impedance measurements [ 50 , 51 ] showed that the room temperature CO sensitivity of SnO 2 /PdO x nanocomposites is precisely due to the participation of such surface OH-groups in the oxidation of chemisorbed carbon monoxide molecules via reaction (5): …”