Benzene Oxidation in Air by an Amine-Functionalized Metal-Organic Framework-Derived Carbon- and Nitrogen-Loaded Zirconium Dioxide-Supported Platinum Catalyst.

To learn more about the behavior of amine (NH 2 )-functionalized metal-organic framework (MOF)-derived noble metal catalysts in the removal of aromatic volatile organic compounds in air, benzene oxidation at low temperatures has been investigated using 0.2-, 0.8-, and 1.5%-platinum (Pt)/Universitetet i Oslo (UiO)-66-NH 2 . The benzene conversion ( X B ) of x %-Pt/UiO-66-NH 2 -R under dry conditions (175 °C) was 23% ( x = 0.2%) < 52% ( x = 0.8%) < 100% ( x = 1.5%): 'R' suffix denotes reduction pretreatment using a hydrogen (10 vol %) and nitrogen mixture at 300 °C for the generation of metallic Pt (Pt 0 ) sites and simultaneous partial MOF decomposition into carbon- and nitrogen-loaded zirconium dioxide. The prominent role of reduction pretreatment was apparent in benzene oxidation as 1.5%-Pt/UiO-66-NH 2 did not exhibit catalytic activity below 175 °C (dry condition). The promotional role of moisture in benzene oxidation by 1.5%-Pt/UiO-66-NH 2 -R was evident with a rise in the steady-state reaction rate ( r ) at 110 °C (21 kPa molecular oxygen (O 2 )) from 1.3 × 10 -3 to 5.0 × 10 -3 μmol g -1 s -1 as the water (H 2 O) partial pressure increased from 0 to 1.88 kPa. In contrast, the activity was lowered with increasing RH due to catalyst poisoning by excess moisture ( r (110 °C) of 6.6 × 10 -04 μmol g -1 s -1 at 2.83 kPa H 2 O (21 kPa O 2 )). Kinetic modeling suggests that X B proceeds through the Langmuir-Hinshelwood mechanism on the Pt/UiO-66-NH 2 -R surface (dissociative O 2 chemisorption and the involvement of two oxygen species in benzene oxidation). According to the density functional theory simulation, the carbon and nitrogen impurities are to make the first X B step (i.e., hydrogen migration from the benzene molecule to the substrate) energetically favorable. The second hydrogen atom from the benzene molecule is also extracted effectively, while the oxygen derived from O 2 facilitates further X B . The Pt 0 sites dissociate the O 2 and H 2 O molecules, while the product of the latter, i.e., free hydrogen and hydroxyl, makes the subsequent X B steps energetically favorable.