Reinvestigation of the Infrared Spectrum of the Gas-Phase Protonated Water Tetramer

Wang, Huan; Agmon, Noam

doi:10.1021/acs.jpca.7b01856

Cited by 28 publications

(29 citation statements)

References 69 publications

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“…The relative intensity of this latter band decreases in parallel with the HPW loading which is indicative of the decrease of hydroxyl groups of TiO 2 covered by HPW units. In the water bending region, the xHPW/Ti acid catalysts show two bands at 1712 and 1620 cm −1 , attributed to the bending O-H vibration of dioxonium H 2 O 5 + and neutral water respectively [34]. The relative intensity of the acid/neutral water ratio in the xHPW/Ti acid catalysts, calculated from the relative area of the bands at 1712 and 1620 cm −1 , is not proportional to the HPW loading (Table 1).…”

Section: Structure and Acidity Of Xhpw/ti Acid Catalystsmentioning

confidence: 99%

Direct Synthesis of Dimethyl Ether from Syngas on Bifunctional Hybrid Catalysts Based on Supported H3PW12O40 and Cu-ZnO(Al): Effect of Heteropolyacid Loading on Hybrid Structure and Catalytic Activity

et al. 2020

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The performance of bifunctional hybrid catalysts based on phosphotungstic acid (H3PW12O40, HPW) supported on TiO2 combined with Cu-ZnO(Al) catalyst in the direct synthesis of dimethyl ether (DME) from syngas has been investigated. We studied the effect of the HPW loading on TiO2 (from 1.4 to 2.7 monolayers) on the dispersion and acid characteristics of the HPW clusters. When the concentration of the heteropoliacid is slightly higher than the monolayer (1.4 monolayers) the acidity of the clusters is perturbed by the surface of titania, while for concentration higher than 1.7 monolayers results in the formation of three-dimensional HPW nanocrystals with acidity similar to the bulk heteropolyacid. Physical hybridization of supported heteropolyacids with the Cu-ZnO(Al) catalyst modifies both the acid characteristics of the supported heteropolyacids and the copper surface area of the Cu-ZnO(Al) catalyst. Hybridization gives rise to a decrease in the copper surface area and the disappearance of the strong acidic sites typical of HPW nanocrystals, showing all hybrids similar acid sites of weak or medium strength. The activity of the hybrids was tested for direct DME synthesis from syngas at 30 bar and 250 °C; only the hybrids with HPW loading higher than 1.4 monolayers showed activity for the direct synthesis of DME, showing that the sample loaded with 2.7 monolayers of heteropolyacid had higher activity than the reference hybrid representative of the most widely applied catalysts based on the combination of Cu-ZnO(Al) with HZSM-5. In spite of the high activity of the hybrids, they show a moderate loss in the DME production with TOS that denotes some kind of deactivation of the acidity function under reaction conditions.

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Section: Structure and Acidity Of Xhpw/ti Acid Catalystsmentioning

confidence: 99%

Direct Synthesis of Dimethyl Ether from Syngas on Bifunctional Hybrid Catalysts Based on Supported H3PW12O40 and Cu-ZnO(Al): Effect of Heteropolyacid Loading on Hybrid Structure and Catalytic Activity

et al. 2020

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“…The proton in water cluster has been conventionally considered to be in two accommodation motifs, the Eigen form 21 (i.e., a hydrated hydronium cation, H 3 O + (H 2 O) 3 ) and the Zundel form 16 (i.e., a proton shared between two water molecules, H 2 O···H + ···OH 2 ), which would induce dramatically different vibrational features near 1000 and 2660 cm −1 , respectively, in the IR spectrum 12 . Agmon and co-workers have studied the IR spectra of protonated water clusters of different sizes by using ab initio molecular dynamics simulations 24 – 27 , which contributed comprehensive understanding of the protonated water structures.…”

Section: Introductionmentioning

confidence: 99%

Towards complete assignment of the infrared spectrum of the protonated water cluster H+(H2O)21

et al. 2021

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The spectroscopic features of protonated water species in dilute acid solutions have been long sought after for understanding the microscopic behavior of the proton in water with gas-phase water clusters H+(H2O)n extensively studied as bottom-up model systems. We present a new protocol for the calculation of the infrared (IR) spectra of complex systems, which combines the fragment-based Coupled Cluster method and anharmonic vibrational quasi-degenerate perturbation theory, and demonstrate its accuracy towards the complete and accurate assignment of the IR spectrum of the H+(H2O)21 cluster. The site-specific IR spectral signatures reveal two distinct structures for the internal and surface four-coordinated water molecules, which are ice-like and liquid-like, respectively. The effect of inter-molecular interaction between water molecules is addressed, and the vibrational resonance is found between the O-H stretching fundamental and the bending overtone of the nearest neighboring water molecule. The revelation of the spectral signature of the excess proton offers deeper insight into the nature of charge accommodation in the extended hydrogen-bonding network underpinning this aqueous cluster.

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“…The large number of studies on the Eigen 56 and Zundel 57 complexes of water with hydronium ion in small clusters are indicative of the challenges in modeling and experiments. [58][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73][74][75][76][77] Because of the large droplets that we study, we model the hydronium ions by an empirical model, where the parameters were taken from. 49 The testing of the model is presented in Fig.…”

Section: Models and Simulation Methodsmentioning

confidence: 99%

Molecular Characterization of the Surface Excess Charge Layer in Droplets

Kwan¹,

Consta²

2020

Preprint

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<div>Charged droplets play a central role in native mass spectrometry, atmospheric aerosols and in serving as micro-reactors for accelerating chemical reactions. The surface excess charge layer in droplets has often been associated with distinct chemistry. Using molecular simulations for droplets with Na+ and Cl- ions we have found that this layer is ≈ 1.5−1.7 nm thick and depending on the droplet size it includes 33%-55% of the total number of ions. Here, we examine the eﬀect of droplet size and nature of ions in the structure of the surface excess charge layer by using molecular dynamics. We ﬁnd that in the presence of simple ions the thickness of the surface excess charge layer is invariant not only with respect to droplet size but also with respect to the nature of the simple ions and it is not sensitive to ﬁne details of diﬀerent force ﬁelds used in our simulations.</div><div> In the presence of macroions the excess surface charge layer may extend to 2.0. nm. For the same droplet size, iodide and model hydronium ions show considerably higher concentration than the sodium and chloride ions. <br></div><div>We also ﬁnd that diﬀerences in the average water dipole orientation in the presence of cations and anions in this layer are reﬂected in the charge distributions. Within the surface charge layer, the number of hydrogen bonds reduces gradually relative to the droplet interior where the number of hydrogen bonds is on the average 2.9 for droplets of diameter < 4 nm and 3.5 for larger droplets. The decrease in the number of hydrogen bonds from the interior to the surface is less pronounced in larger droplets. In droplets with diameter < 4 nm and high concentration of ions the charge of the ions is not compensated only by the solvent polarization charge but by the total charge that also includes the other free charge. This ﬁnding shows exceptions to the commonly made assumption that the solvent compensates the charge of the ions in solvents with very high dielectric constant. The study provides molecular insight into the bi-layer droplet structure assumed in the equilibrium partitioning model of C. Enke and assesses critical assumptions of the Iribarne-Thomson model for the ion-evaporation mechanism. <br></div>

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Reinvestigation of the Infrared Spectrum of the Gas-Phase Protonated Water Tetramer

Cited by 28 publications

References 69 publications

Direct Synthesis of Dimethyl Ether from Syngas on Bifunctional Hybrid Catalysts Based on Supported H3PW12O40 and Cu-ZnO(Al): Effect of Heteropolyacid Loading on Hybrid Structure and Catalytic Activity

Direct Synthesis of Dimethyl Ether from Syngas on Bifunctional Hybrid Catalysts Based on Supported H3PW12O40 and Cu-ZnO(Al): Effect of Heteropolyacid Loading on Hybrid Structure and Catalytic Activity

Towards complete assignment of the infrared spectrum of the protonated water cluster H+(H2O)21

Molecular Characterization of the Surface Excess Charge Layer in Droplets

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