We provide the first observation and characterization of super electrophilic metal cations on a solid support. For Pd/SSZ-13, the results of our combined experimental (Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, high-angle annular dark-field scanning transmission electron microscopy) and density functional theory study reveal that Pd ions in zeolites, previously identified as Pd+3 and Pd+4, are, in fact, present as super electrophilic Pd+2 species (charge-transfer complex/ion pair with the negatively charged framework oxygens). In this contribution, we reassign the spectroscopic signatures of these species, discuss the unusual coordination environment of “naked” (ligand-free) super electrophilic Pd+2 in SSZ-13, and their complexes with CO and NO. With CO, nonclassical, highly positive [Pd­(CO)2]2+ ions are formed with the zeolite framework acting as a weakly coordinating anion (ion pairs). Nonclassical carbonyl complexes also form with Pt+2 and Ag+ in SSZ-13. The Pd+2(CO)2 complex is remarkably stable in zeolite cages even in the presence of water. Dicarbonyl and nitrosyl Pd+2 complexes, in turn, serve as precursors to the synthesis of previously inaccessible Pd+2–carbonyl–olefin [Pd­(CO)­(C2H4)] and Pd+2–nitrosyl–olefin [Pd­(NO)­(C2H4)] complexes. Overall, we show that the zeolite framework can stabilize super electrophilic metal (Pd) cations and show the new chemistry of the Pd/SSZ-13 system with implications for adsorption and catalysis.

The majority of harmful atmospheric CO and NO x emissions are from vehicle exhausts.A lthough there has been success addressing NO x emissions at temperatures above 250 8 8Cw ith selective catalytic reduction technology,e missions during vehicle cold start (when the temperature is below 150 8 8C), are am ajor challenge.H erein, we showw ec an completely eliminate both CO and NO x emissions simultaneously under realistic exhaust flow, using ah ighly loaded (2 wt %) atomically dispersed palladium in the extra-framework positions of the small-pore chabazite material as aC O and passive NO x adsorber.U ntil now,a tomically dispersed highly loaded (> 0.3 wt %) transition-metal/SSZ-13 materials have not been known. We devised ag eneral, simple,a nd scalable route to prepare such materials for Pt II and Pd II . Through spectroscopyand materials testing we showthat both CO and NO x can be simultaneously completely abated with 100 %e fficiency by the formation of mixed carbonyl-nitrosyl palladium complex in chabazite micropore.Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

The conversion of ethylene to ethylidyne on Pt(111) has been studied using density functional periodic slab model calculations. Similar to our recent investigation of this reaction on Pd(111), we considered the following three mechanisms: (M1) ethylene f vinyl f ethylidene f ethylidyne; (M2) ethylene f vinyl f vinylidene f ethylidyne; (M3) ethylene f ethyl f ethylidene f ethylidyne. We systematically compared three coverages of the adsorbate, 1/3, 1/4, and 1/9. Our calculations show that the typical barriers of hydrogenationdehydrogenation reactions on Pt(111), 19-92 kJ mol -1 , are slightly lower than those on Pd(111), 25-120 kJ mol -1 . The barriers of direct 1,2-H shift reactions are much higher, above 160 kJ mol -1 . The surface coverage notably affects the relative barriers of the reactions, by up to 30 kJ mol -1 . Mechanisms M1 and M2 are expected to be competitive. As the barriers of the three elementary steps of mechanism M3 are lower or comparable to the rate-limiting barriers of the other two mechanisms, M3 could be operative when a sufficient concentration of surface hydrogen is present. However, at such conditions one expects the formation of ethane rather than that of ethylidene. On the basis of our calculated vibrational frequencies and reaction barriers, we suggest that an intermediate identified in recent vibrational spectroscopic studies of the title reaction is possibly not ethylidene but perhaps vinyl.

Electronic Supplementary Information (ESI) available: Information includes sketches of all modeled Pt8(CO) complexes in gas phase and some of their energetic and structural characteristics, structure of e-reg/(CO)2 complex, and figure with the changes of the CO stretching frequency versus oxidation state and Bader charge of mononuclear platinum species. See DOI: 10.1039/x0xx00000x The paper addresses possible ambiguities in determination of the state of platinum species by the stretching frequency of a CO probe, which is a common technique for characterization of platinum-containing catalytic systems. We present a comprehensive comparison of the available experimental data with our theoretical modeling (density functional) results of pertinent systems -platinum surface, nanoparticles and clusters as well as reduced or oxidized platinum moieties on ceria support. Our results for CO adsorbed on-top on metallic Pt . This trend corroborates the Kappers-van der Maas correlation derived from analysis of experimental stretching frequency of CO adsorbed on platinum-containing samples on different supports. We also analyzed the effect of the charge of platinum species on the CO frequency. Based on the calculated vibrational frequencies of CO in various model systems, we concluded that the actual state of the platinum species may be mistaken based only on the measured value of the C-O vibrational frequency due to overlapping regions of frequencies corresponding to different types of species. In order to identify the actual state of platinum species one has to combine this powerful technique with other approaches.

We have studied the interaction of water with stoichiometric CeO 2 (111)/Cu(111), partially reduced CeO 2−x /Cu(111), and Pt/CeO 2 / Cu(111) model catalysts by means of synchrotron−radiation photoelectron spectroscopy (SRPES), resonant photoemission spectroscopy (RPES) at the Ce 4d edge, infrared reflection absorption spectroscopy (IRAS), and density functional (DF) calculations. The principal species formed during adsorption of water at 160 K on CeO 2 (111) films is chemisorbed molecular water. On the surface of CeO 2−x water partially dissociates yielding hydroxyl groups. By use of core-level PES, differentiation between chemisorbed water and hydroxyl groups is complicated by the overlap of the corresponding spectral features. Nevertheless, we determined three characteristic indicators for OH groups on ceria: (i) the presence of 1π and 3σ states in valence band (VB) PES; (ii) an increase of the binding energy (BE) separation between the O 1s spectral components of lattice oxygen and OH/H 2 O; (iii) an increase of the amplitude of the Ce 3+ resonance in RPES. Chemisorbed water desorbs below 400 K and hydroxyl groups vanish at 500 K. The most favorable configurations of chemisorbed water and hydroxyl groups have been investigated by DF calculations. Both CeO 2 (111) and CeO 2−x involve strongly tilted H 2 O and OH species which complicate their detection by IRAS. On Pt/CeO 2 , water adsorbs molecularly at 160 K but undergoes partial dissociation during annealing. The dissociation of water is accompanied by spillover of hydrogen to ceria and formation of hydroxyl groups between 180 and 250 K. Above 250 K, decomposition of hydroxyl groups and reverse spillover of hydrogen from ceria to Pt occurs, followed by desorption of molecular water.

On Pd(111), thermal activation of ethylene has been reported to yield ethylidyne. Using more approximate models, a plausible three-step mechanism, ethylene f vinyl f ethylidene f ethylidyne, was recently proposed for this process on the basis of DFT calculations. We employed more elaborate computational models and characterized the thermodynamics and kinetics of the mechanism of ethylene conversion to ethylidyne on Pd(111). We carried out density functional slab-model studies for three coverages of the adsorbate, 1/3, 1/4, and 1/9. The resulting refined potential energy landscape turned out to differ notably from that reported previously: our calculated barriers for the various elementary steps are significantly lower than those of previous studies, and we determined the overall process to be exothermic, in contrast to earlier computational results. We show that the three-step mechanism is thermodynamically and kinetically feasible on Pd(111), with the dehydrogenation of ethylene to vinyl being the rate-limiting step at all coverages considered. Direct conversion of ethylene to ethylidene is unlikely due to a very high barrier. Coverage effects have been found important. At high coverage, the rate-limiting first reaction barrier is ∼50 kJ mol -1 above the desorption energy of ethylene, whereas at low coverages the two energies become comparable.

No abstract

The majority of harmful atmospheric CO and NOx emissions are from vehicle exhausts. Although there has been success addressing NOx emissions at temperatures above 250 °C with selective catalytic reduction technology, emissions during vehicle cold start (when the temperature is below 150 °C), are a major challenge. Herein, we show we can completely eliminate both CO and NOx emissions simultaneously under realistic exhaust flow, using a highly loaded (2 wt %) atomically dispersed palladium in the extra‐framework positions of the small‐pore chabazite material as a CO and passive NOx adsorber. Until now, atomically dispersed highly loaded (>0.3 wt %) transition‐metal/SSZ‐13 materials have not been known. We devised a general, simple, and scalable route to prepare such materials for PtII and PdII. Through spectroscopy and materials testing we show that both CO and NOx can be simultaneously completely abated with 100 % efficiency by the formation of mixed carbonyl‐nitrosyl palladium complex in chabazite micropore.