Effect of Crystallographic Phase (β vs. γ) and Surface Area on Gas Phase Nitroarene Hydrogenation Over Mo2N and Au/Mo2N

Abstract

The catalytic action of Mo 2 N and Au/Mo 2 N has been assessed in the selective gas phase hydrogenation of p-chloronitrobenzene (p-CNB) to p-chloroaniline (p-CAN). The nitrides were synthesised via temperature programmed treatment of MoO 3 in H 2 ? N 2 and Au introduced by deposition-precipitation with urea. We have examined the influence of nitride crystallographic phase (tetragonal b-Mo 2 N vs. cubic c-Mo 2 N) and surface area (7-66 m 2 g-1) on the catalytic response. Catalyst activation by temperature programmed reduction has been monitored and the reduced catalysts characterised in terms of BET area/pore volume, H 2 chemisorption/temperature programmed desorption (TPD), powder X-ray diffraction (XRD), elemental analysis, scanning (SEM) and transmission (TEM) electron microscopy and X-ray photoelectron spectroscopy (XPS) measurements. The formation of band c-Mo 2 N was confirmed by XRD and TEM. c-Mo 2 N exhibits a platelet morphology whereas b-Mo 2 N is characterised by an aggregation of small crystallites. Hydrogen chemisorption and TPD analysis have established a greater hydrogen uptake capacity (per unit area) for b-Mo 2 N relative to c-Mo 2 N, which is associated with surface nitrogen deficiency, i.e. higher surface Mo/N for b-Mo 2 N. Incorporation of Au on both nitrides resulted in an increase in surface hydrogen. The Au phase takes the form of nanoscale particles with a mean size of 7 and 4 nm on b-Mo 2 N and c-Mo 2 N, respectively. Both b-Mo 2 N and c-Mo 2 N promoted the exclusive hydrogenation of p-CNB to p-CAN where the b-form delivered a higher specific (per m 2) rate; the specific rate for c-Mo 2 N was independent of surface area. The inclusion of Au on both nitrides served to enhance p-CAN production.

Supported Molybdenum Carbide and Nitride Catalysts for Carbon Dioxide Hydrogenation

“…In order to compare the nature of the atoms incorporated into the structure, a series of supported molybdenum nitride catalysts were synthesized using method A (MoN A ) or method B (MoN B ) with TiO 2 -P, TiO 2 -D, or ZrO 2 as support ( Table 2). Based on the literature dealing with the synthesis of bulk molybdenum nitride (Ghampson et al, 2012;Perret et al, 2012;Cárdenas-Lizana et al, 2018), the formation of hexagonal β-Mo 2 N is favored when using low GHSV, high heating ramp and low N 2 content in the gas stream (method A) while the opposite conditions usually generate cubic γ-Mo 2 N with high surface area (method B).…”

Effect of support redox character on catalytic performance in the gas phase hydrogenation of benzaldehyde and nitrobenzene over supported gold

“…Gold content was measured by atomic absorption spectroscopy (Shimadzu AA-6650 spectrometer with an air-acetylene flame) from the diluted extract in aqua regia (25% v/v HNO3/HCl). The pH associated with the point of zero charge (pHpzc) of the support was determined using the potentiometric mass titration technique described in detail elsewhere [21]. Temperature programmed reduction (TPR), H2 chemisorption/temperature programmed desorption (TPD), O2 chemisorption and specific surface area (SSA) measurements were conducted on the CHEM-BET 3000 (Quantachrome) unit equipped with a thermal conductivity detector (TCD) for continuous monitoring of gas composition and the TPR Win TM software for data acquisition/manipulation.…”

Controlled nitridation of tantalum (oxy)nitride nanoparticles towards optimized metal-support interactions with gold nanocatalysts

“…8 Thus, the synergy of the above two functions varies the electronic features and catalytic performance of metal nitrides. 9,10 As evidence in catalytic nitroarene hydrogenation, 11,12 the metal-support interactions with gold are promoted by Mo 2 N supports. 9,10 As evidence in catalytic nitroarene hydrogenation, 11,12 the metal-support interactions with gold are promoted by Mo 2 N supports.…”