In Situ Attenuated Total Reflection Infrared (ATR-IR) Study of the Adsorption of NO₂^-, NH₂OH, and NH₄⁺ on Pd/Al₂O₃ and Pt/Al₂O₃

Abstract

In relation to the heterogeneous hydrogenation of nitrite, adsorption of NO2-, NH4+, and NH2OH from the aqueous phase was examined on Pt/Al2O3, Pd/Al2O3, and Al2O3. None of the investigated inorganic nitrogen compounds adsorb on alumina at conditions presented in this study. NO2-(aq) and NH4+(aq) on the other hand show similar adsorption characteristics on both Pd/Al2O3 and Pt/Al2O3. The vibrational spectrum of the NO2- ion changed substantially upon adsorption, clearly indicating that NO2- chemisorbs onto the supported metal catalysts. On the contrary, adsorption of NH4+ does not lead to significant change in the vibrational spectrum of the ion, indicating that the NH4+ ion does not chemisorb on the noble metal but is stabilized via an electrostatic interaction. When comparing the adsorption of hydroxylamine (NH2OH(aq)) on Pd/Al2O3 and Pt/Al2O3, significant differences were observed. On Pd/Al2O3, hydroxylamine is converted into a stable NH2(ads) fragment, whereas on Pt/Al2O3 hydroxylamine is converted into NO, possibly via HNO(ads) as an intermediate.

The influence of water and pH on adsorption and oxidation of CO on Pd/Al2O3—an investigation by attenuated total reflection infrared spectroscopy

“…First, a Pd/Al 2 O 3 powder catalyst was prepared and characterized as described elsewhere in detail. 16,29 The catalyst powder was then deposited on an ATR-IR ZnSe internal reflection element (IRE) and mounted in a home-built in situ ATR-IR stainless steel flow-through-cell as previously described. 10,16,28,29,33 In brief, a 5 wt% Pd/Al 2 O 3 catalyst (dispersion of 45% 16,29 ) was prepared by adsorption of palladium acetylacetonate (Pd(acac)2) (Alfa Aesar) on pre-calcined g-Al 2 O 3 powder.…”

“…16,29 The catalyst powder was then deposited on an ATR-IR ZnSe internal reflection element (IRE) and mounted in a home-built in situ ATR-IR stainless steel flow-through-cell as previously described. 10,16,28,29,33 In brief, a 5 wt% Pd/Al 2 O 3 catalyst (dispersion of 45% 16,29 ) was prepared by adsorption of palladium acetylacetonate (Pd(acac)2) (Alfa Aesar) on pre-calcined g-Al 2 O 3 powder. A suspension was prepared from Pd/Al 2 O 3 in 50 mL of water; the pH was adjusted to 3.5 with nitric acid to stabilize the small alumina particles.…”

“…24 Only a very limited number of studies reported on reactions involving CO in water. 1,19,28,29 In general, detailed mechanistic studies of reactions occurring in water are limited because it is difficult to study heterogeneous catalysts in situ if the reaction is carried out in water. In the gas phase, transmission spectroscopy is a versatile tool to study adsorption and reaction on catalytic surfaces.…”

“…25 Recently, ATR-IR spectroscopic studies at the metal/liquid interface have started to receive attention. 10,11,15,[26][27][28][29][30][31] The adsorption and oxidation of CO and the dissociation of small molecules such as formaldehyde over Pt/Al 2 O 3 catalysts was reported. 31 In addition, ATR-spectroscopic studies of the water-gas shift reaction and methanol reforming over Pt/Al 2 O 3 were combined with kinetic studies.…”

Purification of Waste Water Using Alumina as Catalysts Support and as an Adsorbent

“…In practice, the nitrate and nitrite ions that disappear from the reaction solution are presumed to be converted to N 2 and NH 4 + , without taking the possibility of adsorption onto the catalyst into account. In fact, there is very little information regarding to the nitrate and/or nitrite adsorption onto alumina; however, there have been recent reports regarding such adsorption (Handa et al, 2001, Kney et al, 2004, Ebbesen, et al, 2008. If significant amounts of nitrate or nitrite ions are adsorbed onto an alumina support, then such adsorption phenomena should be taken into consideration when the catalytic activity of denitration is calculated, especially for batch experiments.…”