The Temperature Dependence of Carbon Monoxide Adsorption on a

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C: Surfaces, Interfaces, Porous Materials, and Catalysis

The Temperature Dependence of Carbon Monoxide Adsorption on a High-Silica H-FER Zeolite Miroslav Rubeš, Michal Trachta, Eva Koudelková, Roman Bulánek, Ji#í Klimeš, Petr Nachtigall, and Ota Bludsky J. Phys. Chem. C, Just Accepted Manuscript • Publication Date (Web): 25 Oct 2018 Downloaded from http://pubs.acs.org on October 25, 2018

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The Journal of Physical Chemistry

The Temperature Dependence of Carbon Monoxide Adsorption on a High-Silica H-FER Zeolite Miroslav Rubeša, Michal Trachtaa, Eva Koudelkováb, Roman Bulánekb, Jiří Klimešc, Petr Nachtigalld, and Ota Bludskýa,* aInstitute

of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 162 10 Prague, Czech Republic

bDepartment

of Physical Chemistry, Faculty of Chemical Technology, University of Pardubice, Studentská 573, 532 10 Pardubice, Czech Republic

cDepartment

of Chemical Physics and Optics, Faculty of Mathematics and Physics,

Charles University, Ke Karlovu 3, 121 16 Prague, Czech Republic dDepartment

*

of Physical and Macromolecular Chemistry, Faculty of Science, Charles University, Hlavova 8, 128 40 Prague, Czech Republic

Corresponding author: [email protected]

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The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ABSTRACT The temperature dependence of the isosteric heat of the CO adsorption on a high-silica H-FER zeolite was investigated using microcalorimetry and DFT/CC atomistic simulations. A large change of the experimental heat of adsorption was observed at the zero-coverage limit for the CO/H-FER system (from 32.2 kJ/mol at 200 K to 25.4 kJ/mol at 300 K). This can be explained by a dramatic change in CO dynamics in the 200–300 K temperature range. During our ab initio molecular dynamics simulation at 200 K, the CO molecule is localized; at 300 K the molecule jumps between adjacent Brønsted sites. The only exception has been found for the T4‘‘ site, where the fast desorption of the CO molecule is prevented by a curved ferrierite wall enclosing this site. The previously reported VTIR heat of adsorption of the CO/H-FER with Si/Al 27.5 (28.4(±2) kJ/mol) is consistent with the PBE/CC predictions for individual sites when the statistical distribution of adsorption sites and temperature effects are taken into account.


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1. Introduction Protonic zeolites play a crucial role in oil refining, petrochemistry, and fine chemical production.1-3 Their catalytic activity stems from the presence of Si-O(H)-MIII groups (where MIII is a trivalent heteroatom in the framework), representing a strong Brønsted acid. Much effort has focused on explaining the catalytic diversity of protonic zeolites by means of experimental and theoretical determination of probe-molecule interactions with Brønsted-acid sites. Small gas molecules such as carbon monoxide or dinitrogen are known to form weak hydrogen-bonded complexes with Brønsted protons (HB). Nevertheless, the accurate determination of the probemolecule–HB interactions associated with very low adsorption heats is not an easy task for either experiment or theory. Carbon monoxide adsorption in protonic zeolites has been thoroughly studied using infrared spectroscopy and calorimetry along with contemporary quantum chemistry calculations.4-16 In the most comprehensive study to date, Nachtigall et al. reported a combined FTIR and computational investigation of dinitrogen and carbon monoxide adsorption on protonic high-silica ferrierite (HFER).12 Theoretical calculations at the periodic DFT(PBE) level were employed to determine the location and stability of the ferrierite Brønsted-acid sites and adsorption heats of the adsorbed molecules. Variable temperature IR spectroscopy (VTIR) was used to determine adsorption enthalpies and entropies experimentally. The CO molecule forming linear complexes with the Brønsted OH group pointing towards a sufficiently ample void space showed the largest adsorption heats in the range of 25 to 29 kJ/mol in accord with the VTIR value of 28.4(±2) kJ/mol. It should be noted, however, that the theoretical values were obtained with a semi-local density functional, as a result of which the important non-local (dispersion) contributions of about 10 kJ/mol were neglected. Moreover, the ideal-gas thermal correction used for the conversion of internal energy at 0K into adsorption enthalpies at 200K (-7/2 RT) contradicts the observed temperature dependence of calorimetric heats. While the localized adsorption model17 provides the correct sign of the temperature coefficient, the complex dynamics of the CO molecule adsorbed on the Brønsted-acid site cannot be fully captured by simple statistical mechanical considerations. To achieve quantitative agreement with experimental observations, ab initio molecular dynamics (AIMD) simulations have to be employed.



There are two main limitations of AIMD that need to be considered for extended systems. First, due to a significant increase of the computational demands of electronic structure calculations as compared to force-field based approaches, AIMD can routinely access timescales in the order of tens of picoseconds. That might be sufficient for localized adsorption dynamics on the Brønstedacid site in protonic zeolites, whereas for fully delocalized CO dynamics in pure siliceous materials (in nanoseconds), empirical force fields have to be parameterized prior to molecular dynamics simulations. Second, the accuracy of AIMD is limited by the accuracy of the underlying electronic structure method. At present, theoretical calculations carried out on catalytic systems are mainly based on the density functional theory (DFT) to obtain a reasonably accurate description of the electronic and structural properties of investigated materials at manageable computational costs. The most serious drawback of the commonly used generalizedgradient approximation (GGA) functionals, a failure to account for non-local correlation effects, is now well understood and several strategies for correcting semi-local density functionals have been proposed.18-22 In the case of CO interaction with zeolites, however, none of the commonly implemented dispersion-corrected DFT (DC-DFT) methods seems to provide sufficiently accurate results.4 Hence, a reliable treatment of the CO-HB interaction requires the use of highlevel theoretical approaches such as coupled-cluster with singles, doubles and perturbative triples (CCSD(T)) or advanced DFT approaches based on the random-phase approximation (RPA). At present, the use of highly correlated wavefunction-based methods in atomistic simulations is computationally prohibitive for extended systems. In this study, we have used the DFT/CC correction scheme for accurate calculations of the interaction energies of adsorption complexes.23 The DFT/CC method offers a computationally tractable solution to the aforementioned problems by correcting DFT to coupled-cluster accuracy using suitable interaction models mimicking the electronic properties of the extended system. For zeolites, convenient model systems are the nT clusters used in several previous studies.24-26 To alleviate problems related to the extrapolation of the DFT/CC corrections from small nT clusters to periodic systems, we used the RPA/rSE method for periodic systems to produce reference data for the DFT/CC parameterization.27


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2. Methods 2.1. Experimental section The H-FER zeolite with Si/Al = 27.5, used in this study, was prepared by carefully heating the parent NH4-FER, supplied by Zeolyst International. The sample in the form of fine powder (400 mg) was heated from room temperature to 723 K at a heating rate of 1K/min in the flow of dry nitrogen (25 ml/min) and kept at this temperature for 1 h, after which the gas was switched to dry oxygen with the same flow rate for another 4 h. Finally, the sample was cooled down to room temperature freely in the oxygen flow (5 ml/min). Pure-silica FER (Si-FER) was synthesized from Cab-O-Sil M5 in the presence of pyridine and propylamine in hydrofluoric acid solution. Details can be found in Ref.28 Silicalite (pure-silica MFI zeolite) was synthesized from fumed silica using a mixture of propylamine, trimethylamine and tetramethylamonium bromide in hydrofluoric acid solution.24 The details of the basic characteristics of the materials (XRD, SEM, N2 adsorption isotherms and IR spectroscopy) are reported in the Supporting Information. The heats of CO adsorption on the investigated samples were measured using an isothermal TianCalvet type of microcalorimeter (BT 2.15, Setaram) combined with a purpose-made static volumetric adsorption device. Before the calorimetric experiment, all samples (with the weight of each being 400 mg) were degassed on an ex-situ treatment vacuum line under dynamic vacuum provided by a turbomolecular pump (residual pressure < 10-5 mbar) by slow heating (at the rate of 2.5 K/min) to the target temperature of 723 K and kept at this temperature for 2 h. After cooling down to room temperature, the sample was transferred under vacuum to the calorimetry. The adsorption experiments were carried out at 200 and 300 K (the stability of the temperature during experiment was better than 0.02 K) by the step-by-step dosing of a known amount of carbon monoxide (Linde gas, 99.996 %) to the cell until the equilibrium pressure of 900 mbar was reached for the experiment at 300 K (or 30 mbar at 200K). Each dose was equilibrated for at least 60 min. 2.2. Computational section The periodic DFT calculations for the Si-FER and H-FER systems were performed with the PBEoptimized unit cell (a=19.108 Å, b=14.346 Å, c=7.576 Å, and α=β=γ=900) consisting of 36


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silicon and 72 oxygen atoms. The Brønsted-acid sites were introduced by replacing a silicon atom with aluminum and placing a charge-compensating proton at the nearby oxygen forming the most stable protonic site.12 Throughout this paper, the IZA notation for the four topologically distinct T-atoms (T1 to T4) has been used. Geometry optimizations at the PBE level were converged to 10-2 eV/Å using an energy cutoff of 400 eV for the plane-wave basis. The Γ-point sampling of the Brillouin zone was found to provide sufficiently accurate interaction energies.16 Harmonic frequencies were calculated by the finite-difference method with four displacements (0.005 Å) along each Cartesian coordinate. The ab initio NVT molecular dynamics simulations at the PBE level were performed at 200 K and 300 K with a 0.5fs time step. Since the initial CO position was set near the Brønsted site, the 2.5ps equilibration was found to be sufficient. The production MD simulations were 20 ps for 200 K and up to 80 ps for 300 K. Periodic DFT calculations and ab initio MD simulations were performed using the VASP code with PAW pseudopotentials. In order to account for non-local electron correlation, several dispersion-corrected DFT (DCDFT) approaches were employed (PBE-D18, PBE-XDM19, PBE-TS20, PBE-MBD21, and vdWDF222). We also used random-phase approximation with exact exchange (EXX+RPA, denoted as RPA throughout the article) along with singles correction to correlation energy (rSE)27 and the DFT/CC approach23 (for implementation details, see the Supporting Information) to obtain highly accurate interaction energies. Due to a strong overestimation of the Brønsted-proton interaction with the CO molecule at the PBE level of theory,4 we also investigated the performance of the hybrid PBE0 functional. The cluster calculations were performed for nT…CO complexes (Fig. S1). The cluster results were used in the parameterization of the DFT/CC corrections (see the Supporting Information for more details). The calculations were performed with Dunning’s aug-cc-pVXZ basis sets denoted as AVXZ (X=D,T,Q). The complete basis set (CBS) limit was estimated using the procedure proposed by Halkier et al.29 The counterpoise-corrected CCSD(T)/CBS interaction energies were evaluated as follows:

𝐸[CCSD(T)/CBS] = 𝐸[CCSD(T)/AVDZ] + 𝐸[MP2/CBS] ― 𝐸[MP2/AVDZ] ,


(1)


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where MP2/CBS was obtained from the AVTZ/AVQZ extrapolation. Besides the CCSD(T)/CBS estimates calculated from Eq. 1, we also performed explicitly correlated CCSD(T)-F12 calculations with the VTZ-F12 basis set.30 The cluster calculations were performed using the MOLPRO quantum chemistry package. The corresponding DFT values were calculated using VASP for clusters inside the large periodic box (25×25×25 Å) with the same settings as described in the previous paragraph. Due to extreme computational demands, the cluster RPA/rSE calculations were carried out for the series of smaller periodic boxes of increasing size (10–15 Å) to obtain converged RPA/rSE interaction energies. CO adsorption in pure-silica zeolites (FER and MFI frameworks) was investigated with framework-specific ab initio force fields (AIFFs) obtained by fitting the PBE/CC data (2500 and 1000 points for FER and MFI, respectively). The pairwise interaction potentials were scaled up by a few percent to reproduce the Boltzmann-weighted mean energy calculated for each framework at the PBE/CC level. The heats of adsorption were calculated using Eq. 2, where q stands for the heat of adsorption, 1 is the NVT-averaged total energy of the supersystem (zeolite framework + CO molecule), 0 is the averaged zeolite-only total energy and is the averaged total energy of a single CO molecule at a given temperature 1

― 𝑞 = 〈𝑈1〉1 ― 〈𝑈0〉0 ― 〈𝑈𝑔〉 ― 𝛽.

(2)

After 0.5ns equilibration, three independent 20ns simulations employing a 1.5fs time step were performed using Gromacs31 for the FER and MFI structures optimized by the force field of Bushuev and Sastre.32-33 During these simulations, both the framework and the CO molecule were held rigid, the C–O bond length was set to 1.128 Å using the LINCS algorithm, and the molecule was modeled without any charges. The temperature of simulation (300K) was controlled using the v-rescale algorithm. The short-range vdW and direct-space PME cutoffs were set to 12 Å. The asymptotic contribution to interaction energy from the region between 12 and 30 Å was added as an averaged DFT/CC correction evaluated on a smaller subset of data.


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3. Results and Discussion 3.1. Ab initio modeling: nT..CO cluster models The interaction of the CO molecule with protonic zeolites was investigated using highly correlated wavefunction-based methods (coupled-cluster and Møller–Plesset perturbation theories), approaches based on the random-phase approximation, and several dispersion-corrected DFT methods including two different parameterizations of the DFT/CC method. The results for the nT..CO complexes (Fig. S1) are summarized in Table S1. CCSD(T) calculations have been reported to provide reference-quality (nearly exact) data for solids.34 The errors related to the MP2 extrapolation of correlation energy used in the evaluation of CCSD(T)/CBS binding energies have been estimated from the explicitly correlated CCSD(T)-F12 calculations. It is evident from Table S1 that whenever the MP2 performs reasonably well (e.g. for complexes with perpendicular orientation), the CCSD(T)/CBS values nearly coincide with their CCSD(T)-F12 counterparts. Both sets of CCSD(T) values in Table S1 agree within 0.2 kJ/mol, with the difference being mostly attributable to MP2 extrapolation errors. The RPA (exact-exchange + RPA correlation) method provides a well-balanced description of most bonding types in solids including van der Waals bonding and often improves the results over GGA density functionals. The accuracy of the RPA method is, however, unsatisfactory for adsorbate–adsorbent interactions. Adsorption energies are typically underestimated at the RPA level.35 The results are significantly improved when renormalized singles corrections (rSE) are applied to the RPA.27 In the case of nT..CO complexes, the rSE method approaches the CCSD(T) reference values within expected accuracy (0.2 kJ/mol). It is of crucial importance that the rSE correction to RPA yields reference-quality data for CO–zeolite interactions. While coupledcluster methods for periodic systems have already been implemented, their application to large systems such as zeolites would hardly be practical. To achieve the primary goal of this study, an approach with computational costs of traditional DFT (GGA) must meet the very high computational demands of AIMD. We have employed DCDFT methods based on the PBE density functional and non-empirical vdW-DF2 method. The PBE functional has been chosen on account of its good performance on protonic zeolites, where the insufficient treatment of non-local electron correlation partly compensates for the



overestimation of the CO-HB interaction. The results of geometry optimizations and the corresponding interaction energies are actually better than those of the hybrid PBE0 functional with improved description of the CO–HB binding (cf. Table S3). The DC-DFT methods listed in Table S1 tend to overestimate the nT..CO binding. The binding energy of the most stable 2T..CO complex (perpendicular orientation) is overestimated by 0.6–2.2 kJ/mol with the relative error of 9–32%. Due to the overestimation of the CO–HB interaction, the performance of DC-PBE methods for the 2T-HB..CO complex (the 2T model of Brønsted acid sites) is highly unsatisfactory (Table S3). The PBE/CC parametrizations reported in Tables S1–S3 provide the coupled-cluster quality results for the nT..CO complexes. This might not be so surprising as the nT..CO clusters have been used to evaluate PBE/CC corrections. Only four of these clusters, however, have been used in each parameterization. Since the results of both PBE/CC parameterizations with a different selection of the reference nT..CO models reported in Table S1 are basically indistinguishable, there is no easy way to improve the accuracy of the PBE/CC correction scheme without a reliable and tractable reference method for extended systems. Therefore, the computational results of this work rely mainly on the rSE reference data for a high-silica H-FER zeolite.

3.2. CO adsorption in pure-silica zeolites The accuracy of the PBE/CC methodology has first been verified on pure-silica materials, SiFER and silicalite. Binding energies for CO adsorbed in the ferrierite cage (P-cage) and in the main 10-ring channel are reported in Table 1. The structures of the adsorption complexes were optimized using PBE and PBE-D2 methods. The difference between the PBE and PBE-D2 structures is significant in the tight environment of P-cage with larger dispersion contributions and stronger binding. The performance of the DC-DFT and PBE/CC methods can be assessed by comparison with the rSE results. The overbinding tendency of DC-DFT methods is preserved for the extended systems. The best-performing PBE-D2 method overestimates the 2T model by 0.7 kJ/mol, for the CO/FER system by 2–3 kJ/mol. The non-empirical vdW-DF2 method overestimates the binding energies even more, by 11 kJ/mol. Table S2 shows the difference between two different PBE/CC parameterizations. While the original PBE/CC parameterization36 performs marginally better than PBE-D2, the PBE/CC parameterization reported in Table 1


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yields results much closer to the reference (rSE) values. From now on, we will use the latter as described in the Supporting Information.

As evident from the discussion above, the performance of computationally fast pairwisecorrected DFT methods for systems as large as protonic zeolites cannot be measured only by their accuracy for moderately large cluster models. The extrapolation of the cluster results for firstprinciples methods, such as rSE, should be more robust. Nevertheless, a small deterioration in performance cannot be ruled out; therefore, a comparison with a reliable experiment is highly desirable. The CO interaction with surfaces of siliceous materials is mainly driven by dispersion (cf. PBE binding energies in Tables 1–2) and these materials provide energetically homogeneous adsorption landscapes due to the absence of strong adsorption sites such as Brønsted-acid sites in protonic zeolites. The adsorption process in siliceous zeolites is thus mainly determined by the framework density and the channel geometry and its proper description requires highly accurate force fields parameterized on ab initio calculations to lift the computational constraints of ab initio molecular simulations.24 The procedure is quite tedious, but it offers a direct comparison with experimental data as an alternative to theoretical benchmarks. The experimental and theoretical isosteric heats at zero-coverage limits for silicalite and Si-FER are reported in Table 3. Since the temperature dependence of adsorption heats should be rather small for pure siliceous materials, the experimental heat was measured only for 300 K. The experimental results are depicted in Fig. 1. Due to weak interaction, only a narrow range of the amount of CO adsorbed was measured and the heats were almost constant. The experimental value of 16.9 kJ/mol measured on silicalite is consistent with the value of 17±1 kJ/mol measured previously by Savitz et al. at 195 K.14 The agreement with the PBE/CC theoretical value of 16.8 kJ/mol is rather fortuitous as the calculated isosteric heat strongly depends on the geometry of the zeolite framework. For example, the MFI framework taken from the IZA database yields the value of 16.2 kJ/mol. The experimentally determined heat of adsorption of CO for Si-FER is 18.4 kJ/mol, which is larger than the heat on silicalite in line with higher framework density and smaller channels of the FER structure. The agreement with the PBE/CC theoretical value (17.8 kJ/mol) is reasonable considering all the assumptions involved in our simulation. A more



thorough MD study with a relaxed zeolite geometry would require a highly accurate empirical potential for the description of the framework dynamics.37

3.3. CO interaction with Brønsted-acid sites in high-silica H-FER zeolites The location and stability of Brønsted-acid sites in high-silica H-FER have been investigated by several research groups.12, 16, 38 From 14 possible configurations, only the most stable Brønsted sites for each distinguishable Al position (T1-T4) were considered in this study (Fig. 2). To some extent, the reported relative stabilities of Brønsted sites depend on computational details. The size of the ferrierite unit cell (single vs. double UC) influences the ordering of relative stabilities with the most pronounced effect on T4 sites. For T1–T3 sites, there is a site significantly more stable than other sites with the same Al position regardless of the UC size (Figs. 2a–2c). For the T4 site, the calculation with the double UC favors the T4(Al)-O5-T2(Si) site, while the single UC prefers the T4(Al)-O7-T3(Si) site. The large effect for the T4(Al)-O5-T2(Si) site stems from the strong stabilization of the Brønsted proton inside the six-membered ring (see Fig 2d), which also influences the CO binding at this site (see Ref.12 for more details). Although the most stable “isolated” T4 site is most likely T4(Al)-O5-T2(Si), the Si/Al ratio of 27.5 for the high-silica HFER material investigated roughly corresponds to one Al atom per single UC. From this viewpoint, the calculations of Feng et al.16 are more realistic; therefore, we have used the single UC in AIMD simulations. Both T4 sites are included in Tables 2 and 3, summarizing the results for the CO interaction with H-FER Brønsted sites. The results in Table 2 clearly demonstrate the difficulties with standard DFT-based methods for the description of CO interaction with protonic zeolites. The first problem is the proper treatment of dispersion interactions, where both GGA and hybrid-GGA density functionals spectacularly fail. The second problem is an accurate description of the CO..HB interaction (PBE overbinding). Since both problems are corrected at the PBE/CC level, the calculated binding energies are in very good agreement with the reference data (rSE) for all investigated structures. The third piece of the CO puzzle is the proper evaluation of the thermal correction to the adsorption enthalpy, ΔH0(0 K), calculated as a sum of the electronic interaction energy, ΔEel, and a change in the zero-point vibrational energy. In this work, we have employed single-site AIMD


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simulations at the PBE level corrected a posteriori by the PBE/CC method. The results are summarized in Table 3. The calculated isosteric heats for each Brønsted site are consistent with calorimetric measurements at the zero-coverage limit. Experimental values measured on H-FER at 200 and 300K are reported in Fig 1 (black squares and red circles). It is evident that heats at the zero-coverage limit of 25.4 kJ/mol at 300 K and 32.2 kJ/mol at 200 K are almost constant up to the amount of 0.1 mmol/g of adsorbed CO due to the occupation of the strongest adsorption sites. The experimental values are in very good agreement with theoretical isosteric heats for T1 sites. The large difference between the heats measured at 200 and 300 K can be explained by the analysis of CO dynamics. The plot of instantaneous HB-C and HB-O interatomic distances between the adsorbed CO molecule and the nearest Brønsted-acid site (HB) shows a dramatic change in the CO dynamics going from 200 K to 300 K. Whereas at 200 K the CO molecule is localized at a given site, at 300 K it starts to move from one site to another, spending a significant portion of time in the space between the adjacent adsorption sites (each clipped peak in Fig. 3 corresponds to the CO transfer between the sites). This effect is also responsible for lowering the isosteric heat at 300 K by 7 kJ/mol for the most populated T1 site. Assuming the random Al distribution in the H-FER sample, the population of each Brønsted site T1:T2:T3:T4 should correspond to the site multiplicity (16:8:8:4). Therefore, it can be expected that the contribution from the T2–T4 sites will be statistically smaller than that from the T1 site. At 200 K, the T2 and T3 sites should be indistinguishable for CO with adsorption heats of about 28 kJ/mol. At higher temperatures, the adsorption complex at the T2 site appears to be slightly more localized. The most stable T4(Al)-O5-T2(Si) Brønsted site (T4‘) binds the CO molecule very weakly due to intra-zeolite H-bonding and the large deformation energy required to form the CO adsorption complex.12 The T4(Al)-O7-T3(Si) site (T4‘‘) is thus a preferable binding site for the CO molecule. The very small change of adsorption heats observed for the T4‘‘ site in the range of 200–300 K can be attributed to the cage effect, preventing the desorption of the CO molecule (see Fig. S6 in the Supporting Information). The CO adsorbed on the T4‘‘ site forms a linear complex with the Brønsted OH group pointing towards the curved wall of the ferrierite P-cage. This arrangement ensures that the escaping CO molecule rebounds back to the adsorption site, which significantly lowers the desorption rate at this site.



The differences in CO isosteric heats at individual T sites are also reflected in their dependence on coverage (the amount adsorbed). The experiment at 200 K made it possible to measure isosteric heats up to the adsorbed amount 0.7 mmol/g (H-FER contains 0.51 mmol/g of Brønsted sites determined by a quantitative analysis of ammonia evolved during the heating of the parent NH4-FER). The isosteric heat starts to decrease from the initial heat of ca 32 kJ/mol at the adsorbed amount below 0.1 mmol/g to 21.5 kJ/mol at 0.51 mmol/g, representing 100% coverage (this means that the HB:COads ratio is equal to 1), after which the isosteric heat decreases to the value observed for Si-FER. This is in good agreement with the isosteric heats calculated by MD for individual T sites, ranging from 33.0 kJ/mol for the T1 site to 17.4 kJ/mol for the T4´site. The previously reported heat of CO adsorption on H-FER with the Si/Al ratio of 27.5 determined by the VTIR method (28.4(±2) kJ/mol) is in the range of our measured and calculated values.12 In light of our results, this value can be interpreted as an interplay between the formation of adsorption complexes on various T sites and the temperature effect. The VTIR heat represents the average value obtained for the CO/H-FER system with coverage in the range of 3–70% and at temperatures from 169 to 229 K. This means that weaker adsorption sites are more populated at lower temperatures (and thus higher coverages) than at higher temperatures (and lower coverages). At higher temperatures, only the strongest adsorption sites are occupied, but the isosteric heat is lowered by dynamic effects (e.g. the thermal correction to the adsorption heat).


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4. Conclusions The temperature dependence of the isosteric heat of CO adsorption on high-silica H-FER zeolites has been investigated using microcalorimetry and quantum chemistry atomistic simulations. We have shown that the proper description of the CO adsorption on protonic zeolites requires a highly accurate evaluation of (i) the dispersion interactions between the CO molecule and the zeolite framework, (ii) interactions with Brønsted-acid sites, and (iii) thermal corrections to CO adsorption enthalpy. In this work, we have employed the PBE/CC method parameterized to coupled-cluster and RPA/rSE benchmark data. The accuracy of PBE/CC was first verified on pure-silica materials, Si-FER and silicalite, for which 20ns MD simulations were carried out using AIFFs fitted to PBE/CC data. An excellent agreement between theory and experiment has been found for silicalite. The small discrepancy for Si-FER (0.6 kJ/mol) can be attributed either to the simplifications involved in our simulations (e.g. rigid framework approximation) or to defects in the Si-FER material, occurring in the real material. The large decrease of the experimental heat of adsorption at the zero coverage limit observed for the CO/H-FER system in the temperature range of 200–300K has been rationalized by means of ab initio molecular dynamics. The isosteric heat measured by calorimetry has ranged from 32.2 kJ/mol at 200 K to 25.4 kJ/mol at 300 K. The analysis of instantaneous HB-C and HB-O interatomic distances has indicated a dramatic change in CO dynamics when going from 200 K to 300 K. At 200 K, the adsorbed CO molecule seems to be fully localized during the 80ps simulations, while at 300 K the molecule begins to jump from one acid site to another. For a significant part of the simulation time, the molecule consequently dwells in the space between the adjacent sites where the binding energy corresponds to the average dispersion interaction in the Si-FER material of about 17–18 kJ/mol. The only exception is the T4‘‘ site, where the CO molecule forms a linear complex with the Brønsted OH group pointing towards a void space enclosed by a curved wall of the ferrierite P-cage. As a result, the CO molecule is trapped between the adsorption site and the ferrierite wall, which leads to the lowering of the desorption rate at this site. The previously reported heat of CO adsorption on H-FER with the Si/Al ratio of 27.5 measured by the VTIR method (28.4(±2) kJ/mol) is consistent with the results of this study. The VTIR heat



for the CO/H-FER system, which corresponds to the average value for coverages in the range of 3–70% (at temperatures from 169 to 229 K), can be compared to the theoretically predicted values in the range of 17–33 kJ/mol.


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Acknowledgement This work was supported by the Czech Science Foundation Grant No. 17-07642S. Computational resources were provided by the Ministry of Education, Youth and Sports of the Czech Republic from the Large Infrastructures for Research, Experimental Development and Innovations project (IT4Innovations National Supercomputing Center) and by the CESNET and the CERIT Scientific Cloud (Grants No. LM2015070, LM2015042 and LM2015085). JK is supported by the Primus program of Charles University.

Appendix A. Supporting Data Supporting data associated with this article can be found, in the online version, at http://dx.doi.org/... Implementation of the DFT/CC correction scheme, details of the basic characterization of the investigated materials (XRD, SEM, N2 adsorption isotherms and IR spectroscopy), snapshots from the MD simulation at the T4‘‘ site (P-cage), and the comparison of adsorption models for the CO/H-FER system.



References 1.

Al-Khattaf, S.; Ali, S. A.; Aitani, A. M.; Zilkova, N.; Kubicka, D.; Cejka, J., Recent

advances in reactions of alkylbenzenes over novel zeolites: The effects of zeolite structure and morphology. Catal. Rev.: Sci. Eng. 2014, 56, 333-402. 2.

Busca, G., Acid catalysts in industrial hydrocarbon chemistry. Chem. Rev. 2007,

107, 5366-5410. 3.

Primo, A.; Garcia, H., Zeolites as catalysts in oil refining. Chem. Soc. Rev. 2014,

43, 7548-7561. 4.

Arean, C. O.; Delgado, M. R.; Nachtigall, P.; Thang, H. V.; Rubes, M.; Bulanek,

R.; Chlubna-Eliasova, P., Measuring the Bronsted acid strength of zeolites - does it correlate with the O-H frequency shift probed by a weak base? Phys. Chem. Chem.

Phys. 2014, 16, 10129-10141. 5.

Arean, C. O.; Manoilova, O. V.; Tsyganenko, A. A.; Palomino, G. T.; Mentruit, M.

P.; Geobaldo, F.; Garrone, E., Thermodynamics of hydrogen bonding between CO and the supercage Bronsted acid sites of the H-Y zeolite - Studies from variable temperature IR spectrometry. Eur. J. Inorg. Chem. 2001, 1739-1743. 6.

Delgado, M. R.; Bulanek, R.; Chlubna, P.; Arean, C. O., Bronsted acidity of H-

MCM-22 as probed by variable-temperature infrared spectroscopy of adsorbed CO and N-2. Catal. Today 2014, 227, 45-49. 7.

Feng, P.; Zhang, G. Q.; Zang, K. L.; Li, X. J.; Xu, L. Y.; Chen, X. F., A theoretical

study on the selective adsorption behavior of dimethyl ether and carbon monoxide on HFER zeolites. Chem. Phys. Lett. 2017, 684, 279-284. 8.

Chakarova, K.; Andonova, S.; Dimitrov, L.; Hadjiivanov, K., FTIR study of CO and

N-2 adsorption on Ge FAU zeolites in their Na- and H-forms. Microporous Mesoporous

Mater. 2016, 220, 188-197. 9.

Chakarova, K.; Hadjiivanov, K., H-bonding of zeolite hydroxyls with weak bases:

FTIR study of CO and N-2 adsorption on H-D-ZSM-5. J. Phys. Chem. C 2011, 115, 4806-4817. 10.

Chakarova, K.; Hadjiivanov, K., FTIR study of N-2 and CO adsorption on H-D-

FER. Microporous Mesoporous Mater. 2013, 177, 59-65.


Page 18 of 30

Page 19 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


11.

Limtrakul, J.; Jungsuttiwong, S.; Khongpracha, P., Adsorption of carbon

monoxide on H-FAU and Li-FAU zeolites: An embedded cluster approach. J. Mol. Struct. 2000, 525, 153-162. 12.

Nachtigall, P.; Bludsky, O.; Grajciar, L.; Nachtigallova, D.; Delgado, M. R.; Arean,

C. O., Computational and FTIR spectroscopic studies on carbon monoxide and dinitrogen adsorption on a high-silica H-FER zeolite. Phys. Chem. Chem. Phys. 2009,

11, 791-802. 13.

Rey, J.; Raybaud, P.; Chizallet, C., Ab initio simulation of the acid sites at the

external surface of zeolite beta. ChemCatChem 2017, 9, 2176-2185. 14.

Savitz, S.; Myers, A. L.; Gorte, R. J., Calorimetric investigation of CO and N-2 for

characterization of acidity in zeolite H-MFI. J. Phys. Chem. B 1999, 103, 3687-3690. 15.

Delgado, M. R.; Arean, C. O., Carbon monoxide, dinitrogen and carbon dioxide

adsorption on zeolite H-Beta: IR spectroscopic and thermodynamic studies. Energy 2011, 36, 5286-5291. 16.

Feng, P.; Chen, X. F.; Li, X. J.; Zhao, D.; Xie, S. J.; Xu, L. Y.; He, G. Z., The

distribution analysis on the proton siting and the acid strength of the zeolite ferrierite: A computational study. Microporous Mesoporous Mater. 2017, 239, 354-362. 17.

Al-Muhtaseb, S. A.; Ritter, J. A., A statistical mechanical perspective on the

temperature dependence of the isosteric heat of adsorption and adsorbed phase heat capacity. J. Phys. Chem. B 1999, 103, 8104-8115. 18.

Grimme, S.; Antony, J.; Ehrlich, S.; Krieg, H., A consistent and accurate ab initio

parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu. J. Chem. Phys. 2010, 132, 154104. 19.

Steinmann, S.; Corminboeuf, C., A generalized-gradient approximation exchange

hole model for dispersion coefficients. J. Chem. Phys. 2011, 134, 044117. 20.

Tkatchenko, A.; Scheffler, M., Accurate molecular van der Waals interactions

from ground-state electron density and free-atom reference data. Phys. Rev. Lett. 2009,

102, 6-9. 21.

Tkatchenko, A.; DiStasio, R.; Car, R.; Scheffler, M., Accurate and efficient method

for many-body van der Waals Interactions. Phys. Rev. Lett. 2012, 108, 236402.



22.

Lee, K.; Murray, E.; Kong, L.; Lundqvist, B. I.; Langreth, D. C.; Murray, É. D.,

Higher-accuracy van der Waals density functional. Phys. Rev. B 2010, 82, 081101. 23.

Bludsky, O.; Rubes, M.; Soldan, P.; Nachtigall, P., Investigation of the benzene-

dimer potential energy surface: DFT/CCSD(T) correction scheme. J. Chem. Phys. 2008,

128, 114102. 24.

Rubes, M.; Trachta, M.; Koudelkova, E.; Bulanek, R.; Kasneryk, V.; Bludsky, O.,

Methane adsorption in ADOR zeolites: a combined experimental and DFT/CC study.

Phys. Chem. Chem. Phys. 2017, 19, 16533-16540. 25.

Hermann, J.; Trachta, M.; Nachtigall, P.; Bludsky, O., Theoretical investigation of

layered zeolite frameworks: Surface properties of 2D zeolites. Catal. Today 2014, 227, 2-8. 26.

Hermann, J.; Bludsky, O., A novel correction scheme for DFT: A combined vdW-

DF/CCSD(T) approach. J. Chem. Phys. 2013, 139, 6. 27.

Klimeš, J.; Kaltak, M.; Maggio, E.; Kresse, G., Singles correlation energy

contributions in solids. J. Chem. Phys. 2015, 143, 102816. 28.

Rubes, M.; Koudelkova, E.; Ramos, F. S. D.; Trachta, M.; Bludsky, O.; Bulanek,

R., Experimental and theoretical study of propene adsorption on K-FER zeolites: New evidence of bridged complex formation. J. Phys. Chem. C 2018, 122, 6128-6136. 29.

Halkier, A.; Helgaker, T.; Jorgensen, P., Basis-set convergence in correlated

calculations on Ne, N2, and H2O. Chem. Phys. Lett. 1998, 286, 243-252. 30.

Adler, T. B.; Knizia, G.; Werner, H.-J., A simple and efficient CCSD(T)-F12

approximation. J. Chem. Phys. 2007, 127, 221106. 31.

Berendsen, H. J. C.; Vanderspoel, D.; Vandrunen, R., GROMACS - A message-

passing parallel molecular-dynamics implementation. Comput. Phys. Commun. 1995,

91, 43-56. 32.

Bushuev, Y. G.; Sastre, G., Atomistic simulation of water intrusion-extrusion in

ITQ-4 (IFR) and ZSM-22 (TON): The role of silanol defects. J. Phys. Chem. C 2011,

115, 21942-21953. 33.

Bushuev, Y. G.; Sastre, G., Atomistic simulations of structural defects and water

occluded in SSZ-74 zeolite. J. Phys. Chem. C 2009, 113, 10877-10886.


Page 20 of 30

Page 21 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


34.

Booth, G. H.; Gruneis, A.; Kresse, G.; Alavi, A., Towards an exact description of

electronic wavefunctions in real solids. Nature 2013, 493, 365-370. 35.

Klimes, J., Lattice energies of molecular solids from the random phase

approximation with singles corrections. J. Chem. Phys. 2016, 145, 094506. 36.

Ho Viet, T.; Rubes, M.; Bludsky, O.; Nachtigall, P., Computational investigation of

the Lewis acidity in three-dimensional and corresponding two-dimensional zeolites: UTL vs IPC-1P. J. Phys. Chem. A 2014, 118, 7526-7534. 37.

Fang, H. J.; Awati, R.; Boulfelfel, S. E.; Ravikovitch, P. I.; Sholl, D. S., First-

principles-derived force fields for CH4 adsorption and diffusion in siliceous zeolites. J.

Phys. Chem. C 2018, 122, 12880-12891. 38.

Simperler, A.; Bell, R. G.; Anderson, M. W., Probing the acid strength of Bronsted

acidic zeolites with acetonitrile: Quantum chemical calculation of H-1, N-15, and C-13 NMR shift parameters. J. Phys. Chem. B 2004, 108, 7142-7151.



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Table 1. The binding energies of CO in pure-silica ferrierite (in kJ/mol).a CO location

geometry

rSEb

PBE/CCb

DC-DFTc

P-cage

PBE PBE-D2

13.4 (12.1) 17.2 (14.5)

13.9 (2.9) 17.8 (2.2)

16.1–24.3 19.3–28.3

main channel

PBE PBE-D2

13.6 (11.8) 13.9 (12.0)

14.8 (2.6) 15.1 (2.5)

17.0–25.4 17.2–25.7

2T model

CCSD(T)

6.9 (5.6)

7.0 (2.3)

7.5–9.1

a Deformation

energies are not included. and PBE values for rSE and PBE/CC, respectively, are given in parentheses. c PBE-D2, PBE-D3BJ, PBE-XDM, PBE-TS, PBE-MBD and vdW-DF2 (see Table S1 for more details). b RPA


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Table 2. The binding energies of CO in H-FER zeolite (in kJ/mol).a CO location

PBE0

rSEb

PBE/CCb

DC-DFTc

T1 T2 T3 T4‘ T4‘‘

25.6 25.7 26.3 25.0 26.6

39.6 (31.3) 39.0 (32.8) 37.1 (30.5) 36.0 (30.9) 37.6 (32.3)

39.9 (28.4) 38.7 (28.3) 37.3 (29.1) 35.6 (27.4) 37.6 (29.5)

47.3–54.2 45.7–52.7 44.8–51.3 42.6–49.2 44.9–52.1

2T model

24.2

26.1 (21.0)

25.7 (26.4)

27.9–32.4

a Deformation

energies are not included. and PBE values for rSE and PBE/CC, respectively, are given in parentheses. c PBE-D2, PBE-D3BJ, PBE-XDM, PBE-TS, PBE-MBD and vdW-DF2 (see Table S1 for more details). b RPA



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Table 3. The electronic energies, enthalpies and isosteric heats of CO adsorption in H-FER zeolite (in kJ/mol).a System (site)

ΔEel

ΔH0(0 K)

H-FER (T1) (T2) (T3) (T4‘) b (T4‘’)

-36.7 -31.7 -34.6 -23.9 -35.2

-33.6 -28.5 -30.4 -20.1 -32.3

Si-FER silicalite aE

qst (MD) 200 K 33.0 27.7 28.4 17.4 30.0

300 K 26.0 22.6 21.9

qst (Experiment) 200 K 300 K 32.2 25.4

28.4 17.8 c 16.8 c

el and

18.4 16.9

ΔH0 (0 K) were calculated at the PBE/CC level. Ab initio MD simulations at the PBE level were used for the CO/H-FER system to evaluate temperature corrections to ΔH0 (0 K). b The weakly bound CO..H complex; the isosteric heat has not converged during the 80ps simulation at 300 K. B c MD simulations (3x20 ns) were carried out with AIFF parametrized to PBE/CC data.


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Figure Captions

Figure 1. The heat of CO adsorption on H-FER at 200 K (black squares) and 300 K (red circles), silicalite at 300 K (green point-up triangles) and Si-FER at 300 K (blue point-down triangles) as a function of the amount adsorbed. Figure 2. The adsorption complexes of CO with the most stable Brønsted-acid sites (T1–T4) in H-FER. Figure 3. The instantaneous HB–C (blue) and HB–O (red) interatomic distances between the adsorbed CO molecule and the nearest Brønsted-acid site (HB).



Figure 1

40

Qads (kJ/mol)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 30

35

30

25

20

15 0.00

0.05

0.2

nads (mmol/g)


0.4

0.6

0.8

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Figure 2

a

O2

b

T1

O3

T2

T1

O6 O2

T2

T1

c

T1

O1 T1

O1

T3

d

T4

O5

T2

O7




Page 28 of 30

Page 29 of 30

Figure 3

HB-CO distance [Å]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


200K

300K time [ps]



TOC Graphics


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The Temperature Dependence of Carbon Monoxide Adsorption on a

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