New insights into the effect of nitrogen incorporation in Mo: catalytic hydrogenation vs. hydrogenolysis

The catalytic effect of nitrogen incorporation into Mo on hydrogenation (of -NO2 to -NH2 in nitrobenzene to aniline) and hydrogenolysis (of -C?O in benzaldehyde to toluene) processes has been assessed. Bulk Mo was prepared by temperature programmed reduction of MoO3 (in H-2 to 933 K) and -Mo2N (confirmed by powder XRD) subsequently synthesised by Mo nitridation in N-2/H-2. Two intermediate samples (MoN-1 and MoN-2) with different Mo/N ratio were prepared by altering the duration (1 and 2 h) of the nitridation step. XPS analysis revealed a nitrogen surface enrichment (Mo/N = 2.2 0.9 from MoN-1 to -Mo2N) relative to the bulk (Mo/N = 5.1 2.5). Incorporation of N did not affect morphology and each sample exhibited (by SEM analysis) aggregates (

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

Fernando Cardenas Lizana, Lioubov Kiwi, Daniel André Samuel Lamey, Vincent Laporte

The catalytic action of Mo2N and Au/Mo2N 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 MoO3 in H-2 + N-2 and Au introduced by deposition-precipitation with urea. We have examined the influence of nitride crystallographic phase (tetragonal beta-Mo2N vs. cubic gamma-Mo2N) 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 beta- and gamma-Mo2N was confirmed by XRD and TEM. gamma-Mo2N exhibits a platelet morphology whereas beta-Mo2N is characterised by an aggregation of small crystallites. Hydrogen chemisorption and TPD analysis have established a greater hydrogen uptake capacity (per unit area) for beta-Mo2N relative to gamma-Mo2N, which is associated with surface nitrogen deficiency, i.e. higher surface Mo/N for beta-Mo2N. Incorporation of Au on both nitrides resulted in an increase in surface hydrogen. The Au phase takes the form of nano-scale particles with a mean size of 7 and 4 nm on beta-Mo2N and gamma-Mo2N, respectively. Both beta-Mo2N and gamma-Mo2N promoted the exclusive hydrogenation of p-CNB to p-CAN where the beta-form delivered a higher specific (per m(2)) rate; the specific rate for gamma-Mo2N was independent of surface area. The inclusion of Au on both nitrides served to enhance p-CAN production.

Springer US2012

An examination of catalyst deactivation in p-chloronitrobenzene hydrogenation over supported gold

Fernando Cardenas Lizana, Lioubov Kiwi, Daniel André Samuel Lamey, Xiaodong Wang

The stability of Au/Al2O3 in the continuous gas phase (423 K) hydrogenation of p-chloronitrobenzene (p-CNB) to p-chloroaniline (p-CAN) has been investigated over an inlet H-2/p-CNB = 4-390, i.e. from close to stoichiometry to H2 far in excess. The catalyst (activated unused and spent) has been characterised with respect to specific surface area (SSA)/porosity, temperature programmed reduction (TPR), powder XRD, H-2 chemisorption, STEM, XPS, elemental analysis and TGA-DSC measurements. Activation of Au/Al2O3 by TPR in hydrogen generated a narrow Au size distribution (1-8 nm, mean = 3.6 nm) with evidence (from XPS) of (support -> metal) charge transfer to generate surface Au delta-. Exclusive p-CAN production was achieved under conditions of kinetic control, which were established by parameter estimation and experimental variation of contact time, catalyst particle size and p-CNB/catalyst ratio. A temporal decline in activity was observed that was more pronounced at H-2/p-CNB

Elsevier2014

Surface Reactions are Crucial for Energy Storage

Elsa Callini, Shunsuke Kato, Philippe Mauron

Reactions between gas molecules, e.g. H-2 and CO2 and solids take place at the surface. The electronic states and the local geometry of the atomic arrangement determine the energy of the adsorbate, i.e. the initial molecule and the transition state. Here we review our research to identify the surface species, their chemical state and orientation, the interaction with the neighbouring molecules and the mobility of the adsorbed species and complement the experimental results with thermodynamic modelling. The role of the Ti was found to be a bridge between the charged species preventing the individual movement of the ions including charge separation. The Ti has no catalytic effect on the hydrogen sorption reaction in borohydrides. The physisorption of molecular hydrogen is too weak at ambient temperature to reach a significant hydrogen storage density. The addition of a hydrogen dissociation catalyst to a nanoporous material with a large specific surface area may potentially enable the spillover of hydrogen atoms from the metal catalyst to the surface of the porous material and chemisorb on specific sites with a much higher binding energy compared to physisorption. The intercalation of alkali metals in C-60 fullerenes increases the interaction energy of hydrogen with the so-called metal fullerides significantly. Sterical diffusion barriers by partial oxidation of the surface of borohydrides turned out to redirect the reaction path towards pure hydrogen desorption and suppress the formation of diborane, a by-product of the hydrogen evolution reaction from borohydrides previously undetected. The combination of a newly developed gas controlling system with microreactors allows us to investigate complex reactions with small quantities of nano designed new catalytic materials. Furthermore, tip-enhanced Raman spectroscopy (TERS) will allow the investigation of the reactions locally on the surface of the catalyst and the near ambient pressure photoelectron spectroscopy enables analysis of the surfaces in ultra-high vacuum and in situ interaction with the adsorbates i.e. while the reaction takes place. This brings us in a unique position for the investigation of the heterogeneous reactive systems. The mechanism of the Ti catalysed hydrogen sorption reactions in alanates was recently established based on spectroscopic investigations combined with thermodynamic analysis of the transition states.

Schweizerische Chemische Gesellschaft2015

Surface Reactions are Crucial for Energy Storage

Elsa Callini, Shunsuke Kato, Philippe Mauron

Schweizerische Chemische Gesellschaft2015