Ligand/cluster/support catalytic complexes in heterogeneous ultrananocatalysis: NO oxidation on Ag₃/MgO(100)

Abstract

In the present work we explore via first-principles simulations whether the ligand/cluster/support catalytic complex generated by CO oxidation over silver trimers deposited on the regular MgO (100) surface -i.e. a Ag 3 /carbonate or Ag 3 (CO 3 )/MgO(100) species -can be used as a catalyst in a different reaction: the selective oxidation of NO to NO 2 (or NOox). The Ag 3 (CO 3 )/MgO(100) complex is first shown to be reasonably stable at room temperature in terms of both disaggregation and sintering, and that it can be generated from Ag 3 adsorbed onto an oxygen vacancy defect of the regular MgO (100) surface under oxidation conditions. It is then found that the Ag 3 (CO 3 )/MgO(100) species transforms under NOox conditions into an even more complex aggregate, a mixed carbonate/double-nitrite Ag 3 (CO 3 )(NO 2 ) 2 /MgO(100) species, which can then act as an efficient catalyst of NOox. It is noteworthy that under NOox reaction conditions a different ligand/cluster/support catalytic complex is formed with respect to the original COox one. These findings prove the diversity of the catalytic chemistry of subnanometer (or ultranano) metal clusters deposited on oxide substrates, associated with the formation of many different ligand/cluster/support aggregates, the vast amount of combinatorial possibilities thus opening, and the need for computational approaches to perform systematic structural and stoichiometric searches in order to cope with such a multiform diversity.

Theoretical Investigation of Photoinduced Processes in Subnanometer Oxide-Supported Metal Catalysts

“…Alumina-supported silver nanoparticles of a few tens nanometer in size are typically used in the industrial context, 78,79 but the reaction can be conducted efficiently also over subnanometer cluster catalysts, as in our previous studies on Ag 3 cluster catalysts supported on the MgO(100) regular surface. 39,40,80 As discussed in detail in section 2, here we focus exclusively on the rate-determining step of the EtOx mechanism on Ag 3 (CO 3 )(C 2 H 4 ), i.e., the step:…”

“…the barriers for the other steps being sufficiently low that the population of the corresponding intermediates can be considered as negligible) and we modify the catalyst of our original study 39 in two different ways, studying (i) Ag 3 (HCO 3 )(C 2 H 4 ) 2 (O) and (ii) Ag 3 (CO 2 F)(C 2 H 4 ) 2 (O) aggregates supported on the regular MgO(100) surface, and possibly how they might realize the conclusive catalytic step and evolve the C 2 H 4 O molecule as a photoassisted process. Moreover, since this "Ag 3 (XCO x )-(C 2 H 4 ) 2 (O) → Ag 3 (XCO x )(C 2 H 4 ) + C 2 H 4 O" step can actually be realized either as a single-step process or as a two-step process in which (1) the aggregate first rearranges to an oxametallocycle species to allow for oxygen-adatom migration from one C 2 H 4 to the other, followed by (2) the detachment of the C 2 H 4 O epoxide molecule and its evolution into the gas phase, in the case of Ag 3 (CO 2 F)(C 2 H 4 ) 2 (O) we calculated both the initial configuration and its isomeric oxametallocycle variant with the migrated O-adatom.…”

“…This is an example of and corresponds to the idea of using a ligand/cluster/support catalytic complex from one reaction as the catalyst in a different but akin reaction. 39 It should be stressed that Ag 3 (CO 3 ) does not need CO and O 2 to form, but it will be in any case generated directly in situ under EtOx conditions via reaction of gas-phase CO 2 (an unavoidable side-product in the oxidation of organic species) with Ag 3 (O) intermediates. 41 S1 and S2.…”

Synthesis and Catalytic Application of Silver Nanoparticles Supported on Lactobacillus kefiri S-Layer Proteins

“…Computational methods can explore intermediates and transition energy states that otherwise may be ignored in experimental studies. Theoretical simulation analysis of the different catalytic aspects (size, support, composition, intermediate reagents and products) in relation to the catalytic activity has been evaluated for different reactions involving AgNPs [36][37][38][39]. DFT is a widespread method, which can help us to understand the stability and electronic properties of nanoparticles, their adsorption modes on support surfaces, and to elucidate mechanisms and reaction rates for different reactions taking place on the catalyst surface, which together with experimental studies would allow the development of new catalysts, more efficient and in a more rational way [40].…”

Pentameric PdAu and PdPt nanoparticles on the MgO(1 0 0) surface and their CO and O2 adsorption properties

“…The mapping of the potential energy surface indicated that monomer diffusion at room temperature is unlikely on both supports. Sementa et al [22] found that the intermediate carbonate species Ag 3 (CO 3 ) formed on the MgO(1 0 0) surface during the oxidation of CO on supported silver trimers and is probably the actual catalyst. They also investigated whether such a species may be the catalyst for various other reactions.…”