Lewis Acid Synergy in Methanol-to ... - ACS Publications

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Letter

Brønsted/Lewis Acid Synergy in Methanol-to-Aromatics Conversion on Ga-Modified ZSM-5 Zeolites as Studied by Solid-State NMR Spectroscopy Pan Gao, Qiang Wang, Jun Xu, Guodong Qi, Chao Wang, Xue Zhou, Xingling Zhao, Ningdong Feng, Xiaolong Liu, and Feng Deng ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.7b03211 • Publication Date (Web): 27 Nov 2017 Downloaded from http://pubs.acs.org on November 27, 2017

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Brønsted/Lewis Acid Synergy in Methanol-to-Aromatics Conversion on Ga-Modified ZSM-5 Zeolites as Studied by Solid-State NMR Spectroscopy Pan Gao,†,‡,¶ Qiang Wang, †,¶ Jun Xu,*, † Guodong Qi, † Chao Wang, † Xue Zhou, †,‡ Xingling Zhao, †,‡ Ningdong Feng, † Xiaolong Liu, † Feng Deng*, †

†

State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics,

National Center for Magnetic Resonance in Wuhan, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, P. R. China. ‡

University of Chinese Academy of Sciences, Beijing 100049, P. R. China.

Abstract：：1H-71Ga internuclear spatial proximity/interaction between Brønsted acid site (BAS) and cationic Ga species (Lewis acid sites) in Ga-modified ZSM-5 zeolites that leads to a synergic effect in the methanol-to-aromatics (MTA) conversion was identified with solid-state NMR spectroscopy. The internuclear distance between BAS and Ga species was measured, which is similar to that of a neighboring BAS pair located in the six-membered rings of ZSM-5. The Brønsted acidity of the Ga-modified zeolite was considerably enhanced due to the synergic effect, and the synergic active sites were quantified by 1H-71Ga double-resonance solid-state NMR which shows correlation with the aromatics selectivity in the MTA reaction.

KEYWORDS: zeolites, active site, methanol conversion, solid-state NMR, aromatics, Synergic effect

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With the up-surging demand and increasing depletion of oil reserves, enormous interest has been drawn to the sustainable production of large commodity chemicals such as methylbenzenes, especially BTX (benzene, toluene, xylene), via renewable resources. Among various routes based on alcohols and hydrocarbons,1 the methanol-to-aromatics (MTA) over metal-modified zeolites provides a promising alternative to the oil process.2 In particular, Zn- or Ga-modified ZSM-5 zeolites have attracted intensive studies for the MTA reaction because of their distinct performance toward selective formation of aromatics.2c, 3 Considerable efforts have been devoted to understanding the active sites in the MTA reaction on the metal-modified zeolites, which however still remains unclear. It is well-accepted that the introduction of metals on zeolites leads to the formation of strong Lewis acid sites, which promotes the dehydrogen-aromatization process.2a,

4

The dehydro-cyclization of alkene intermediates formed in the MTA

process can be significantly enhanced by an effective removal of hydrogen atoms as H2, promoting the formation of aromatics.2b,

3b, 4

Concurrently, the generation of

alkane byproducts via traditional H-transfer reactions could be largely suppressed, leading to an increased selectivity to aromatics. Both cationic metal species (Ga3+) and/or metal oxides (Ga2O3) have been reported to be capable of promoting the dehydrogen-aromatization process on Ga-modified ZSM-5 zeolites.3b, 4 However, the previous work on alkene aromatization over the zeolites indicated that the metal species was effective in the dehydrogenation-aromatization process only in the presence of BAS.5 The elimination


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of BAS by K+ ion exchange or titration with pyridine resulted in a nearly complete loss of activity,5-6 suggesting that metal species and BAS might operate in a concerted fashion in the aromatization. In addition,2c, 3a, 3b, 7 the importance of the close spatial proximity between metal species and BAS has been widely noted in the MTA reactions. For example, Hutchings and co-workers2c,

3a, 3b

demonstrated that a

significant enhancement in aromatics during the MTA reaction over a mixture of β-Ga2O3 and H-ZSM-5 could only be achieved when both components were in intimate contact. This implies that a synergic effect between Ga species and BAS is probably present in in Ga modified ZSM-5 to promote the MTA reaction. Although the synergic effect of Ga-modified zeolites is often considered, its detailed mechanism is still poorly understood. Solid-state NMR is a powerful tool for probing the acid sites on zeolites.8 The spatial proximity/interaction between Lewis (extra-framework aluminum) and Brønsted (bridging SiOHAl) acid sites in dealuminated zeolites has been successfully explored by two-dimensional 1H-1H, 27Al-27Al double-quantum magic angle spinning (DQ-MAS) NMR.9 Very recently, 1H-67Zn hetero-nuclear interactions between Zn2+ ions and Brønsted acid sites over Zn-modified ZSM-5 zeolites were identified by high-field

67

Zn NMR spectroscopy, and correlated to the enhanced C-H bond

activation of methane.10 Herein, we for the first time provide deep insights into the local structure of synergic active sites on a Ga-modified ZSM-5. By using 1H-71Ga double-resonance solid-state NMR, we show the direct detection of spatial proximity/interaction between cationic Ga species and BAS. The active/acid site


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synergy arising from the spatial interaction is demonstrated by the enhanced acid strength of Ga-modified zeolites. The quantification of the synergic active sites allows us to correlate them to the aromatics selectivity in the MTA reaction. Ga-modified ZSM-5 (Si/Al=12.5) samples were prepared by mechanically mixing gallium oxide with H-ZSM-5 or wetness impregnation method, denoted as Ga2O3/ZSM-5 and Ga/ZSM-5(IM), respectively. The Ga/ZSM-5(IM) sample was further subject to a reduction-oxidation treatment under H2-O2 flow and the resultant sample was denoted as Ga/ZSM-5(redox) (see details in the supporting information). The Ga loading was determined to be ca. 6 wt% for all the samples by ICP analysis. X-ray diffraction and

27

Al and

29

Si MAS NMR characterizations showed that the

crystal structures of ZSM-5 (MFI type) zeolite are well maintained on all the Ga-modified samples (Figure S1 and S2). Figure 1 shows the product distribution of MTA reactions over parent H-ZSM-5 and different Ga-modified ZSM-5 zeolites. Ga2O3/ZSM-5 and H-ZSM-5 exhibit typical hydrocarbons product distributions with relatively low concentration of both aromatics (13.4 %, mainly toluene, xylene and trimethylbenzene) and C2-4 alkanes (12 %) (Figure 1a and 1b). The influence of Ga species on the MTA reaction was evident for Ga/ZSM-5(IM) and Ga/ZSM-5(redox), reflected by the increase of selectivity to aromatics and the decline of alkenes. In particular, Ga/ZSM-5(redox) has a selectivity of ca. 50% for aromatics. Interestingly, the amount of H2 detected in the product stream concurrently increases (Figure 1b), corresponding to the promotion of the dehydrogen-aromatization process by the Ga species. Note that the distribution


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of ethene exhibits a reverse trend to that of C3-4 alkenes (Figure 1a). Considering the dual cycle model proposed for methanol conversion,11 the pronounced aromatic-based reaction route facilitated by the enhanced light aromatics should be responsible for the increase of ethene,12 while the formation of C3-4 alkenes regulated by the long alkenes is suppressed.

Figure 1. The selectivity of alkanes and alkenes (a) and aromatics (b) of MTA reaction over parent H-ZSM-5 and different Ga-modified ZSM-5 samples. The normalized H2 (to H-ZSM-5) production is plotted in (b).

In order to explore the local structure of Ga species on the modified zeolites,

71

Ga

QCPMG (quadrupolar Carr-Purcell Meiboom-Gill)13 MAS NMR experiments were performed (Figure 2a). The 71Ga QCPMG NMR spectrum of Ga2O3/ZSM-5 exhibits a signal with a typical second-order quadrupolar lineshape and an isotropic chemical shift at 0 ppm (Figure 1a), due to octahedrally coordinated Ga atom from Ga2O3 particles.14 Both Ga/ZSM-5(IM) and Ga/ZSM-5(redox) produce two 71Ga signals with isotropic chemical shifts at 58 and 190 ppm (Table S1). The two spectra were fitted using a Gaussian isotropic model distribution (the more general Czjzek distribution).


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15

The lack of quadrupolar lineshape of the 58 ppm signal as well as the linewidth

broadening is an indication of the formation of high dispersed amorphous Ga2O3 particles on the two samples, in consistent with the absence of the reflections from Ga2O3 particles in the XRD patterns (Figure S1). The appearance of an additional signal at 190 ppm indicates the formation of Ga species in lower coordination. Since the isomorphous substitution of framework Al by the Ga species does not likely occur as supported by

27

Al and

29

Si NMR experiments (Figure S2), the signal can be

ascribed to cationic GaO+ species, probably in its hydrous state, e.g. Ga(OH)2+, which substitutes the acidic proton of BAS and resides on its conjugate-base site (Si-O--Al).16 The cationic GaO+ species has been well characterized by XAFS on Ga-modified ZSM-5 zeolites. Rodrigues et al. suggested from the EXAFS spectra of Ga-modified H-ZSM-5 zeolites prepared by impregnation the formation of isolated/atomically dispersed oxidic gallium species along with the condensed Ga species.17 The in situ EXAFS study of Ga/ZSM-5 prepared by chemical vapor deposition (CVD) of GaCl3 on H-ZSM-5 showed that oxidative and reductive treatments lead to the coordination of GaO+ species to zeolite frameworks.18 By comparing the spectra of Ga/ZSM-5(IM) and Ga/ZSM-5(redox), the 190 ppm signal on Ga/ZSM-5(redox) is relatively increased with respect to the 58 ppm signal (Table S1). This indicates the transformation of Ga species from Ga2O3 particles to GaO+, which is in consistent with previous DRIFT and EXAFS characterizations.17-19 On Ga/ZSM-5(redox), the gallium oxide would be partially gasified during high temperature reduction treatment and subsequently react with the BAS in zeolite


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micropores leading to the increase of cationic Ga species.

Figure 2. (a) 71Ga QCPMG MAS NMR spectra of Ga2O3/ZSM-5, Ga/ZSM-5(IM) and Ga/ZSM-5(redox). The isotropic chemical shifts are indicated on the top of the peaks. (b)

1

H MAS NMR spectra of H-ZSM-5, Ga2O3/ZSM-5, Ga/ZSM-5(IM) and

Ga/ZSM-5(redox).

To gain insight into the formation of Ga species on ZSM-5, 1H MAS NMR experiments were conducted (Figure 2b). Three signals are observed at 4.3, 2.9 and 2.2 ppm in the 1H MAS NMR spectrum of parent H-ZSM-5, corresponding to Brønsted acidic protons (SiOHAl, bridging hydroxyl group), extra-framework AlOH and non-acidic SiOH,8a respectively. For Ga2O3/ZSM-5, the three hydroxyl groups including the BAS remain almost unchanged as compared to the parent H-ZSM-5. Whereas for Ga/ZSM-5(IM), about 12% decrease of the BAS is ascertained by comparing the integral area of the peak at 4.3 ppm, suggesting that a small amount of


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the acidic proton of BAS were substituted by the formed GaO+ species during the impregnation process. A significant decline (46%) in the amount of BAS occurs Ga/ZSM-5(redox) is associated with the considerable increase of the cationic Ga species as observed by

71

Ga NMR (Figure 1a). Note that a small shoulder peak

appears at 1.3 ppm in the

1

H MAS NMR spectra of Ga/ZSM-5(IM) and

Ga/ZSM-5(redox), corresponding to the formation of GaOH group. The GaO+ species on Ga-modified ZSM-5 zeolites has been ascribed to the strong Lewis acid sites.17 The NH3-TPD (Figure S3) together with FTIR spectra of adsorbed pyridine (Figure S4) indicate that the amount of BAS is reduced particularly on Ga/ZSM-5(redox) with the generation of strong Lewis acid due to GaO+ species, in consistence with our 71Ga and 1H NMR results. The key point of the synergy effect is the spatial proximity of Ga species and BAS

on

zeolites.

1

H-71Ga

symmetry-based

rotational-echo

saturation-pulse

double-resonance (S-RESPDOR)20 experiments were performed to probe the spatial proximity which is based on the internuclear dipolar interaction/distance. Proton signals will suffer strong dipolar dephasing during the irradiation of

71

Ga when Ga

nuclei are in close proximity to protons, resulting in reduced 1H signals. A ∆S/S0 value expressed as (S0-S)/S0 (S and S0 represent the signal intensity with and without dipolar irradiation, respectively) is used to describe the degree of 1H-71Ga dipolar dephasing, characterizing the dipolar interaction and spatial proximity between protons and Ga atoms. For Ga2O3/ZSM-5 (Figure 3a), no proton is in close proximity to Ga species as none of the three 1H signals exhibits any observable 1H-71Ga dipolar


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dephasing. This is probably because the Ga2O3 particles are too large to enter the zeolite channel where the BAS is mainly located. On the contrary, an extremely

Figure 3.

1

H-71Ga S-RESPDOR NMR spectra (a, b, c) of Ga2O3/ZSM-5,

Ga/ZSM-5(IM) and Ga/ZSM-5(redox) with a recoupling time of 12 ms, and 1H-71Ga S-RESPDOR built-up curves (d, e, f ) of the BAS, AlOH and GaOH obtained from Ga/ZSM-5(redox) fitted by analytical formula. DIS and rH-Ga represent the dipolar interaction constant and internuclear distance of 1H-71Ga spin pair respectively.

weak 1H-71Ga dipolar dephasing effect is observable for Ga/ZSM-5(IM) as reflected by the weak signals in the difference spectrum (∆S) (Figure 3b). The weak signals are confirmed to be caused by dipolar interactions rather than the instability of NMR instrument via a control experiment (Figure S5). The result indicates the presence of spatial interactions between the protons of the four hydroxyl groups and Ga species, but the neighboring 1H-71Ga pairs should be in low concentration on this sample.


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Interestingly, for Ga/HZSM-5(redox), a strong 1H-71Ga dipolar dephasing effect is evident for the BAS (Figure 3c), indicating that a moderate amount of neighboring BAS-Ga pairs is formed. The cationic Ga species in ZSM-5 channels should be involved in the formation of neighboring BAS-Ga pairs. Note that in addition to BAS, the other protons from AlOH, SiOH amd GaOH also show dipolar interactions with 71

Ga atoms to different extents (Figure 3c), which suggests that these hydroxyl groups

are in different close proximity to the Ga species. The spatial interactions between protons and Ga species were further quantitatively analyzed. The 1H-71Ga S-RESPDOR signal build-up curves (∆S/S0 fraction versus recoupling time) of Ga/ZSM-5(redox) for BAS, AlOH and GaOH reflect the internuclear distance (Figure 3d-f); the closer the internuclear distance (the stronger the spatial interaction) is, the faster the maximum dipolar dephasing will reach. The recoupling time for BAS and GaOH to reach a maximum dipolar dephasing is ca. 12 and 2.4 ms respectively, while the maximum dephasing is not achieved for AlOH even at a recoupling time of 18 ms. The stronger interaction in GaOH is likely due to the short 1H-71Ga internuclear distance in this species. The AlOH group may reside farther away from Ga species as reflected by the weak interaction between 1H with 1

71

Ga. For comparison, the BAS exhibits a moderate

H-71Ga nuclear distance which is between that for GaOH and AlOH species.

Specifically, the 1H-71Ga nuclear distance was extracted by simulating the dephasing built-up curves (Figure 3 and Figure S6-S8), which is 3.04, 5.05, 6.72 Å for GaOH, BAS and AlOH, respectively. Note that a reasonable analysis of the spatial interaction


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between SiOH and Ga species is not feasible due to the weak ∆S/S0 value for the silanol signal. Since each cationic GaO+ would be formed by removing one acidic proton from a BAS and reside on its conjugated base site (Si-O--Al), the formation of a neighboring BAS-GaO+ pair (H+ and GaO+) that has been confirmed by our 1H-71Ga S-RESPDOR experiments requires another BAS in close proximity to the GaO+ cation. It was reported that the neighboring BAS pairs could be generated in large quantity

on

H-ZSM-5,

which

mainly

exist

as

an

AlSiSiAl

sequence

(next-next-nearest-neighboring Al, NNNNAl) in the six-membered ring (6 MR) at the channel intersections.21 Our previous experimental work demonstrated that the average distance between neighboring BAS sites in H-ZSM-5 was ca. 4.5 Å,22 in consistent with the theoretically predicated distance (ca. 5 Å) between the BAS pairs of NNNNAl in the 6MR.21b To get further information on the neighboring BAS-Ga pair, 2D 1H-1H SQ-DQ MAS NMR23 experiments were performed on parent H-ZSM-5 and Ga-modified samples (Figure 4). A strong autocorrelation peak (4.3, 8.6) ppm characterizing the neighboring BAS pair was observed on Ga2O3/ZSM-5 which is similar to that of parent H-ZSM-5 (Figure 4a and 4b), suggesting that the BAS pair remains almost unchanged in Ga2O3/HZSM-5. A slight decline of the intensity of this correlation peak in the spectrum of Ga/ZSM-5(IM) indicates the reduction of neighboring BAS pairs after the introduction of gallium (Figure 4c). Note that this characteristic correlation peak disappears completely in Ga/ZSM-5(redox) (Figure 4d), implying that most of


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the remaining BAS are no longer in close proximity or present in pairs. The isolation

Figure 4. 1H-1H SQ-DQ MAS NMR spectra of (a) H-ZSM-5, (b) Ga2O3/ZSM-5, (c) Ga/ZSM-5(IM) and (d) Ga/ZSM-5(redox).

of the BAS should be resulted from the substitution of acidic protons by Ga species. This supports our observation on the formation of BAS-Ga pairs via the 1H-71Ga S-RESPDOR NMR spectroscopy. Taking the

1

H-1H SQ-DQ and

1

H-71Ga

S-RESPDOR NMR results together, the distribution of Brønsted acid sites and Ga species on the samples can be illustrated in Figure 5.


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Figure 5. Schematic distributions of Brønsted acid sites (acidic protons) and Ga species in the zeolite channels of (a) H-ZSM-5, (b) Ga2O3/ZSM-5, (c) Ga/ZSM-5(IM) and (d) Ga/ZSM-5(redox).

The 1H-71Ga distance (5.05 Å) of BAS-Ga pairs derived from the S-RESPDOR experiment is comparable to the average 1H-1H distance (4.5 Å) of BAS pairs. Therefore, the BAS-Ga pair may reside similarly as the BAS pair, with the BAS and GaO+ being associated with the NNNNAl in the 6MR of zeolite channel. The 1H-1H SQ-DQ MAS NMR spectra also show that the introduction of Ga species has almost no significant influence on the spatial proximity of SiOH groups as no obvious change is visible on the corresponding autocorrelation peak at (2.2, 4.4) ppm. The influence of the spatial proximity/interaction between Ga species and BAS on the acidic property of Ga-modified H-ZSM-5 zeolites was further explored. [D5]pyridine is a well-established NMR probe to measure the Brønsted acid strength of zeolites.8a, 24 Figure 6 shows the 1H MAS NMR spectra of H-ZSM-5 and Gamodified samples loaded with [D5]pyridine. The poor-resolved signals ranging from 1.9 to 4.3 ppm correspond to SiOH, AlOH and a small amount of BAS respectively that are inaccessible to pyridine molecules; the 8.7 and 8.1 ppm signals can be attributed to the formation of hydrogen bonds between pyridine and non-acidic SiOH;


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the low-field main signals at 15.6 and 19 ppm are due to the protonated pyridine on BAS.8a Interestingly, a new shoulder peak at 13.1 ppm appears in the 1H MAS spectra of [D5]pyridine adsorbed on Ga/ZSM-5(IM) and Ga/ZSM-5(redox), but it is absent in those of H-ZSM-5 and Ga2O3/ZSM-5. For [D5]pyridine adsorbed on the BAS of zeolites, pyridine ion complexes are usually formed with 1H chemical shifts in the range of 12-20 ppm, and a smaller 1H chemical shift indicates a stronger Brønsted acid strength.24 Therefore, the observation of the 13.1 ppm signal demonstrates that the acid strength of some BAS is considerably enhanced on Ga/ZSM-5(IM) and Ga/ZSM-5(redox), due to the synergic effect of BAS and Ga species which is generated by their spatial proximity/interaction. In our previous study on the bifunctional Zn/ZSM-5 catalyst, the similar effect on the acidity enhancement was also observed due to the spatial interaction between Zn2+ ions and BAS of zeolite.10 The enhanced acidity of BAS induced by the synergic effect would benefit all the dehydogen-aromatization processes in the MTA reaction such as alkene methylation, cyclization and stabilization of cyclic carbenium intermediates,25 thus facilitating the formation of aromatics.


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Figure 6. 1H MAS NMR spectra of [D5]pyridine adsorbed (a) H-ZSM-5, (b) Ga2O3/ZSM-5, (c) Ga/ZSM-5(IM) and (d) Ga/ZSM-5(redox). The asterisks denote spinning sidebands.

Hutchings and co-workers have found that the amount of Ga species on ZSM-5 zeolite significantly affect the activity of the modified catalyst in the MTA reaction.3a We have known that the formation of BAS-Ga pairs depends on the BAS pairs on ZSM-5, which can be regulated by the Si to Al ratio (SAR) of zeolite.26 Two Ga/ZSM-5(IM) and Ga/ZSM-5(redox) catalysts with the same loading of 6 wt% Ga were also prepared by using a H-ZSM-5 zeolite with a SAR of 50. The 1H-1H SQ-DQ MAS NMR spectra (Figure S9) show that the BAS pairs are notably reduced by comparing the autocorrelation signal intensity at (4.3, 8.6) ppm to those of the samples with a SAR of 12.5 (Figure 4a). This would accordingly result in the decrease of the concentration of BAS-Ga pairs on the corresponding Ga/ZSM-5(IM) and


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Ga/ZSM-5(redox) samples. In order to probe the BAS-Ga pairs, the

1

H-71Ga

S-RESPDOR experiment was also performed on the Ga/ZSM-5(redox) with high SAR (Figure S10). Based on the method we developed for the quantification of synergic active sites by double-resonance solid-state NMR spectroscopy10, the concentration of BAS-Ga pairs was determined for the two Ga/ZSM-5(redox) samples with different SAR (Table 1). The BAS-Ga pairs notably declines from 102.2 to 14 µmol/g when the SAR increases from 12.5 to 50. This change produces a considerable influence on the MTA reaction, i.e., the selectivity to aromatics is significantly reduced from ca. 50 % to 23% on Ga/ZSM-5(redox) with the SAR increasing from 12.5 to 50 (Figure 1b and S11). The similar case is also found for Ga/ZSM-5(IM); the selectivity to aromatics decreases from ca. 22 % to 12%. These results indicate that the formation of aromatics is closely correlated with the amount of BAS-Ga pairs. Table 1. Concentration of BAS and BAS/Ga pairs on Ga/ZSM-5(redox) samples with different Si/Al ratios. Brønsted acid site

Maximum dephasing

BAS/Ga pair a

(µmol/g)

fraction (%)

(µmol/g)

Ga/ZSM-5(redox)

a

Si/Al=12.5

476.8

6.4

102.2

Si/Al=50

143.6

2.9

14.0

see details for the calculations in the supporting information.

In summary, in this work, the neighboring BAS/Ga species have been directly identified for the first time by

1

H-71Ga double-resonance solid-state NMR

spectroscopy on Ga-modified ZSM-5 zeolites. The internuclear interaction/distance of


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BAS/Ga pairs was experimentally measured. The synergic effect generated by the spatial interaction/proximity between BAS and Ga species brings about an enhanced Brønsted acidity. The quantification of the synergic BAS/Ga pairs allows us to correlate them with the aromatics selectivity in the MTA reaction. The results presented herein are helpful for the mechanistic understanding of the synergic effect of active sites in the MTA reaction and may provide a new avenue for unraveling the chemical properties of various metal-modified bifunctional catalysts.

ASSOCIATED CONTENT Supporting Information Details of sample preparation, characterizations and catalytic testing; XRD patterns, 27

Al and 29Si MAS NMR spectra, NH3-TPD, FTIR spectra and 1H-71Ga S-RESPDOR

simulations.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]; *E-mail: [email protected]. ¶

These authors equally contribute to this work

ORCID Jun Xu: 0000-0003-2741-381X Feng Deng: 0000-0002-6461-7152 Notes


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The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (Grants 21622311, 21473245, 21603265, 21210005 and 21733013) and key program for frontier science of the Chinese Academy of Sciences (QYZDB-SSW-SLH027).

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