SilicaâAlumina Catalysts with

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Hydrogenation of Acetophenone on Pd/Silica-Alumina Catalysts with Tunable Acidity: Mechanistic Insight by In Situ ATR-IR Spectroscopy Mengmeng Chen, Nobutaka Maeda, Alfons Baiker, and Jun Huang ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.8b00169 • Publication Date (Web): 30 May 2018 Downloaded from http://pubs.acs.org on May 30, 2018

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ACS Catalysis

Hydrogenation of Acetophenone on Pd/Silica-Alumina Catalysts with Tunable Acidity: Mechanistic Insight by In Situ ATR-IR Spectroscopy

Mengmeng Chena, Nobutaka Maedab,c,, Alfons Baikerb,* and Jun Huanga*

a

Laboratory for Catalysis Engineering, School of Chemical and Biomolecular Engineering,

The University of Sydney, NSW 2006, Australia b

Institute for Chemical and Bioengineering, Department of Chemistry and Applied

Biosciences, ETH Zurich, Hönggerberg, HCl, CH-8093 Zurich, Switzerland c

Present address: Gold Catalysis Research Center, State Key Laboratory of Catalysis, Dalian

Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, People’s Republic of China

ACS Paragon Plus Environment

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ABSTRACT Understanding the cooperative action of metal and acid sites of bifunctional catalysts is essential for developing more efficient catalysts for greener chemical processes. We used in situ ATR-IR

spectroscopy in tandem with modulation excitation spectroscopy (MES) and

phase-sensitive detection (PSD) to examine the functioning of Pd/silica-alumina (Pd/SA) catalysts with different acidity of the support in the liquid phase hydrogenation of acetophenone (AP). The spectroscopic studies revealed that AP was adsorbed on the Pd surface in η1 (O) configuration and initially hydrogenated to 1-phenylethanol (PE) on the metallic Pd sites. On the Pd surface PE was less strongly adsorbed than AP. PE was preferentially adsorbed on the acidic silica-alumina support via the C-OH group and subsequently dehydrated to styrene on the acidic sites. Hydrogen originating from dissociative adsorption on Pd sites is proposed to hydrogenate part of the formed styrene to ethylbenzene (EB). The intermediate styrene had a short life-time under hydrogenation conditions. Increasing the support acidity by raising the atomic fraction of aluminum (Al x100%/(Al + Si)) in SA from 0-70 % promoted the styrene production, which in turn strongly enhanced the EB yield from 17.3% on Pd/silica to 54.3% on Pd/SA-70, respectively.

KEYWORDS: Chemoselective hydrogenation, aromatic ketones, bifunctional Pd/silicaalumina, reaction mechanism, role of acid sites, in situ attenuated total reflection infrared spectroscopy, modulation excitation spectroscopy, phase-sensitive detection.


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1. INTRODUCTION Solid acids supported noble metal catalysts are widely used for the hydrogenation and hydrogenolysis of ketones and alcohols in fine-chemical synthesis and bio-oil upgrading. Acidic supports promote various reaction processes including chemoselective hydrogenation, dehydration/hydrogenolysis, and hydrocracking. Amorphous silica-alumina (SA) is a popular support from natural abundent elements, and its acidity can be well tuned by adjusting the silica/alumina ratio, thereby offering bifunctionality to metal catalysts.1-2 Tuning the support acidity strongly enhances the catalytic performance of supported Pt, Pd and other noble metal catalysts for the chemoselective liquid phase hydrogenation and hydrodeoxygenation of unsaturated ketones.3-5 Acidic supports can induce ionic effects on metal surfaces and affect the surface electronic properties promoting dissociation of hydrogen resulting in enhanced hydrogenation rates.6 Changing the surface electronic properties of noble metal nanocatalysts by the acidic supports also can affect the adsorption and desorption of unsaturated ketones on the metal surface, which are crucial for the surface reaction. The adsorption mode and its strength can thus significantly influence the reaction pathway. The hydrogenation of acetophenone (AP) can serve as a suitable model for the chemoselective hydrogenation of an aromatic ketone due to competing hydrogenation of an aromatic ring and a carbonyl group. Basically, three mechanisms have been suggested for the transformation of the carbonyl group: (i) Hydrogenation followed by dehydration yielding a C=C double bond and its further hydrogenation. (ii) Hydrogenation of the carbonyl compound to the corresponding alcohol via hydrogenolytic rupture of the C–O bond yielding a hydrocarbon (C–C=O→C–C–OH→C–C), and (iii) the direct hydrogenolysis of the C=O bond (C–C=O→C–C). 7 In the gas-phase hydrogenation of AP over Pt supported on various oxides (silica, η-alumina, titania, and SA), SA supported catalysts showed high yield to ethylbenzene (EB), suggesting


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a bifunctional reaction involving dehydrogenation of PE on the acid support and hydrogenation of C=C bonds on Pt.8 As the majority of chemoselective hydrogenations are conducted in the liquid phase, understanding of liquid phase reactions is crucial for the development of this research area. Liquid-phase hydrogenations differ in various aspects from gas-phase hydrogenations, including the use of solvents, lower diffusion rates, limited concentration of dissolved hydrogen, contacting time, and adsorption/desorption behavior. In a previous study of the liquid phase hydrogenation of AP on Pt/γ-Al2O3 (γ-Al2O3 is a popular catalyst for alcohol dehydration), no PE dehydration and bifunctional action was observed.9 In the past decade flame spray pyrolysis (FSP) has gained considerable attention as a powerful and versatile method for catalyst synthesis. 10 In a previous study, we examined the influence of the silica to alumina ratio of FSP synthesized Pd/SA catalysts11 on their acidity and catalytic performance in the chemoselective liquid phase hydrogenation of AP.4 The aim of the present work is to gain deeper insight into the mechanism of this reaction with a particular focus on the role of the support surface acidity in the reaction pathway. For this purpose we examined the hydrogenation of AP to EB on Pd nanoparticles supported on SA with different silica/alumina ratios by means of in situ ATR-IR spectroscopy12 in tandem with modulation excitation spectroscopy (MES) and phasesensitive detection (PSD). Combining ATR-IR and MES significantly enhances the signal to noise (S/N) ratio and also allows the discrimination between active surface species and spectators.13-16

2. EXPERIMENTAL SECTION Detailed descriptions of the different experimental procedures are given in the cited references and the Supporting Information (SI). 2.1. Catalyst synthesis


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Catalysts consisting of 5wt% Pd supported on amorphous silica-alumina (SA) with different ratio of Si/Al, designated as Pd/SA-X, where X corresponds to the fraction of Al (Al at% = Al x100%/(Al + Si)) in the silica–alumina, were prepared by flame spray pyrolysis (FSP), as reported previously.17 2.2 Surface acidity The surface acidity of the Pd/SA catalysts, characterized by the concentration of Brϕnsted acid sites, was determined by means of 1H MAS NMR spectroscopy. The concentrations of Brϕnsted acid sites of the catalysts were 0, 7.9×10-2, and 10.3×10-2 mmol/g for Pd/silica, Pd/SA-15, and Pd/SA-70, respectively.17 2.3. In situ ATR-IR combined with Modulation-Excitation Spectroscopy The preparation of the thin catalyst layer and its immobilization on the ZnSe internal reflection element (IRE, bevel of 45º, 52 mm×20 mm×2 mm, Crystran Ltd.) as well as the procedure used for the in situ ATR-IR measurements coupled with MES were similar as reported in ref. 9. In all ATR-IR investigations n-hexane was used as solvent, which was saturated either with helium (adsorption-desorption experiments) or hydrogen (hydrogenation experiments) and the temperature was 60oC, as in the catalytic tests. 2.4 Catalytic tests Acetophenone (AP) (Sigma-Aldrich, 99%) hydrogenation was carried out in a magnetically stirred (500 rpm) stainless steel autoclave at 60oC using 20mg of freshly reduced catalyst, 0.5 mmol of AP and 6 ml of n-hexane solvent.

3. RESULTS AND DISCUSSION 3.1 Catalytic Behavior The results of the catalytic tests on SA supported Pd catalysts with different aluminum content in chemoselective hydrogenation of acetophenone are summarized in Figure 1 and


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Table S1. Clearly, the support acidity could enhance the activity of Pd/SA catalysts in AP hydrogenation. AP conversion after 5 min was only 2.9% on Pd/silica, whereas it was 8.8% and 11.9% on Pd/SA-15 and Pd/SA-70, respectively. This could be attributed to the propensity of the acid supports to pull out electrons from the supported metal particles thereby generating ionic effects on the metal surface, which enhance the activity of the catalysts. After 1h reaction time, AP conversion was around 95% on all Pd/SA catalysts. Possible products were ethylcyclohexane (EC), ethyl benzene (EB), cyclohexyl methyl ketone (CMK), 1-cyclohexylethanol (CE), and 1-phenylethanol (PE). Pd/SA catalysts showed high chemoselectivity for C=O hydrogenation and no or only very small amount of EC, CMK, and CE have been observed during the reaction. On Pd/silica and Pd/SA-15 PE was the only product after 5 min and was further hydrogenated to EB at longer reaction times. This indicates the significance of consecutive hydrogenation steps in the reaction pathway, AP to PE followed by PE to EB, rather than the one-step hydrogenolysis. As shown in Figure 1, the support acidity had a stronger influence on EB selectivity, than on AP conversion. This is traced back to the strong effect of the support acidity on the dehydration of PE to styrene, while some assistance of the hydrogenolytic process of PE OH groups cannot be ruled out.

Figure 1. Acetophenone (AP) hydrogenation on Pd/silica and Pd/SA catalysts at 60oC: (a) AP conversion vs. reaction time; (b) EB selectivity vs. reaction time.


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The following in situ ATR investigations provide deeper insight into the role of support acidity for improvement of EB selectivity. 3.2 In situ ATR-IR studies of reaction pathway 3.2.1 Adsorption and hydrogenation of acetophenone on Pd/silica and Pd/silica-alumina AP adsorption and desorption was followed on Pd/silica and Pd/SA catalysts with different aluminum content at the reaction temperature of 60oC. Vibrational bands used to identify the species involved in AP hydrogenation were based on the IR spectra of neat AP, PE, and EB shown in Figures S1-3. Figure 2 shows the phase-domain in situ ATR-IR spectra monitored during AP adsorption and desorption on Pd/silica (2a), Pd/SA-15 (2b) and Pd/SA-70 (2c). The band at 1670 cm-1 is ascribed to the C=O stretching vibration of AP adsorbed on the support, while that at 1697 cm-1 is due to the C=O stretching mode of AP adsorbed on Pd in the η1 (O) configuration (1682 cm-1 for pure AP).9 AP adsorbed on the support via the Xsensitive benzene mode gave rise to a band at 1276 cm-1. Signals at 1365 cm-1 in Figure 2 are caused by the bending mode of CH3.18,19 Bands due to the C=C stretching vibrations of the phenyl group appear at 1600 cm-1, 1583 cm-1 and 1450 cm-1 in Figure 2a, and at 1598 cm-1, 1581 cm-1, and 1450 cm-1 in Figures 2b and 2c.20


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Figure 2. Phase-domain IR spectra collected during AP (2 mM) adsorption and desorption on (a) Pd/silica, (b) Pd/SA-15, and (c) Pd/SA-70. Figure 2a shows an in-phase angle φPSD = 320° of AP absorption bands with a phase-delay of 40° (360°-320°) for Pd/silica while for Pd/SA-15 (Figure 2b), the corresponding values are φPSD = 330° and 30° (360°-330°). For Pd/SA-70 (Figure 2c) φPSD is 340° with a phase delay of 20° (360°-340°). Positive absorption bands at φPSD = 320° indicate that the rate of adsorption and desorption is slower than that of species at φPSD = 0° resulting in a time delay, i.e., phase delay of 40° (360° − 320°).22 The rate of AP adsorption-desorption on the catalysts therefore obeys the order Pd/SA-70 > Pd/SA-15 > Pd/silica, indicating that the support acidity affects the reactant adsorption-desorption processes.


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Time domain IR spectra recorded during AP hydrogenation on the Pd/silica reference catalyst are presented in Figure 3. Note that hardly any new signals due to products were observed, corroborating the slow initial AP hydrogenation rate on Pd/silica, in line with the results of the catalytic tests (AP conversion of 2.9% after 5 min in Figure 1a and Table S1). The band indicating AP adsorbed on Pd in η1(O) configuration (C=O stretching mode at 1697 cm-1) is hardly discernible in Figure 3 due to the low concentration of this species during AP reaction with H2 on Pd and accordingly the initial main product PE (100% selectivity after 5min) was only barely adsorbed on silica.

Figure 3.Time-resolved IR spectra of AP (2 mM) hydrogenation on Pd/silica. (a) spectra; (b) 2D surface plot.


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To clarify the effect of the support surface acidity, the hydrogenation of AP on Pd/SA-15 and Pd/SA-70 was investigated in the same way as for the Pd/silica reference catalyst. The corresponding time domain spectra are shown in Figures 4 and 5, respectively. In contrast to the behaviour of the silica-supported catalyst (Figure 3), new bands appeared at 1207 cm-1, 1812 cm-1, 1886 cm-1 and 1959 cm-1, indicating PE formation when AP hydrogenation started. These signals are due to combination bands of C-H bending modes of the PE aromatic ring, which was adsorbed on the acidic supports. Note that these signals (PE production and adsorption on the support) progressively increased until 187.5s while the intensity of the band at 1670 cm-1 (C=O stretching mode of AP adsorbed on the support) peaked at 180s and then decreased until 187.5s. Furthermore, the band at 1697 cm-1 (AP on Pd in η1 (O) configuration) became saturated at 150s and moderately decreased with rising bands due to PE production..


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Figure 4. Time-resolved IR spectra of AP (2 mM) hydrogenation on Pd/SA-15. (a) spectra; (b) 2D surface plot. For AP hydrogenation on Pd/SA-70, IR spectra (Figure 5) resembled to those observed with Pd/SA-15. The bands of produced PE continuously grew till 187.5s, whereas the intensity of the band of AP adsorbed on the support peaked at 165s (180s on Pd/SA-15) and then decreased up to 187.5s. The spectra recorded during hydrogenation of AP on SA supported Pd (Figure 4 and 5) indicate that AP adsorbed on the Pd surface in η1 (O) configuration and


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was initially hydrogenated to 1-phenylethanol (PE) on the metallic Pd sites. A possible scenario explaining the results presented in Figures 4 and 5 is that AP adsorbed on the support was replaced by the produced PE (competitive adsorption) and diffused or desorbed and readsorbed onto the Pd surface. On Pt/γ-alumina, PE was earlier found to replace AP on the support during hydrogenation, thereby promoting diffusion of AP to the metal surface for hydrogenation.9 Co-adsorption of AP and PE showed that PE was more strongly adsorbed on the Lewis acid γ-alumina compared to AP. This contrasts the behaviour of AP and PE co-adsorption on Pd/SA investigated in this work. Figures S4-6 show that PE could not replace AP on the SAs surfaces. Thus different co-adsorption behaviour of AP and PE is observed for Pd/SA and Pt/alumina, which has a bearing on the outcome of the hydrogenation reaction. Interestingly, even on SA supports with higher acidity PE could not replace AP in competitive AP and PE adsorption experiments, but the increase of surface acidity promoted the adsorption of PE, as shown in Figures S4-6. In addition, Figure 2 shows that an increase of the support acidity could enhance the rate of AP adsorption-desorption on Pd/SA catalysts (the rate of AP adsorption-desorption follows Pd/SA-70 > Pd/SA-15 > Pd/silica). Therefore, the supports with higher acidity are likely promoting the transfer of AP to the metal surface for the hydrogenation driven by the adsorption induced concentration gradients on the surface. This could explain the shorter time (165s) required for the band of AP adsorbed on the support of Pd/SA-70 for reaching maximum intensity, compared to 180s on Pd/SA-15. This behaviour is also in accordance with the enhanced AP conversion observed in the hydrogenation of AP on Pd/SA compared to Pd/silica.


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Figure 5. Time-resolved IR spectra of AP (2 mM) hydrogenation on Pd/SA-70. (a) spectra; (b) 2D surface plot.

3.2.3 Adsorption and hydrogenation of 1-phenylethanol on Pd/SA catalysts As shown in the catalytic tests (Figure 1 and Table S1) and in situ ATR-IR investigations, the chemoselective hydrogenation of the AP C=O bond resulting in PE was the dominant reaction in the initial period of AP hydrogenation on Pd/SA catalysts. In a consecutive step PE is further hydrogenated to EB via hydrogenation of the C-OH bond or other products by the hydrogenation of the aromatic ring. In order to attain deeper knowledge about these consecutive hydrogenation steps, PE adsorption and hydrogenation on Pd/SA catalysts were investigated. Figure 6a shows the time-domain IR spectra recorded during PE adsorption on Pd/silica. The band of the C=C


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stretching vibration is observed at 1494 cm-1, and that of the deformation mode of the PE phenyl ring at 1205 cm-1.

20, 21

Bands of the C-H out of plane mode of the PE benzene ring

appear at 1951 cm-1, 1882 cm-1 and 1810 cm-1.24 Perceptibly, the PE aromatic ring was also adsorbed on the catalyst surface. Signals at 1666 cm-1 and 1585 cm-1 are considered to belong to PE because these two small signals were also discernible with neat liquid PE (Figure S2). Only PE was involved in adsorption-desorption, no transformation to new products was observed. The corresponding phase-domain ATR-IR spectrum is shown in Figure S7 confirming that no new species appeared during adsorption of PE on Pd/silica because different species should show different kinetic behavior and in-phase angles. In Figure S7, all absorption bands possess the same in-phase angle φ = 0º, therefore, all vibrational modes should belong to PE. When applying H2 saturated n-hexane, a similar time-domain ATR-IR spectrum (Figure 6b) as presented in Figure 6a was obtained. No new products could be detected, confirming the result of the catalytic tests (Table S1). PE hydrogenation was very slow on Pd/silica and virtually no products have been observed in the first few minutes. Similarly, as with Pt supported on Lewis acid alumina9, PE was hardly dehydrated to styrene on Pd/silica. On the alumina support PE was more strongly adsorbed and replaced AP during AP hydrogenation, but no EB was produced when hydrogenation proceeded until 1 h reaction time and the aromatic ring was involved in hydrogenation with the production of CMK and CE.9 On Pd/silica, PE was hydrogenated to EB with nearly no hydrogenation of aromatic rings (Table S1). The weak acidic SiOH groups on the silica support11 may have contributed to the hydrogenation. As shown in Figure 1 and Table S1, the selectivity and yield of EB were significantly enhanced with increasing support acidity.


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Figure 6. (a) Time-resolved IR spectra of PE (2 mM) adsorption on Pd/silica at 60oC. (b) Time-resolved IR spectra of PE (2 mM) hydrogenation on Pd/silica.

The time-domain IR spectra of PE adsorption on Pd/SA-15 (Figure 7a) showed new but negative going bands at 1656 cm-1 and 1575 cm-1 due to styrene, which gradually changed with increasing PE adsorption, indicating that styrene was produced by dehydration of PE adsorbed on Brϕnsted acid sites of the support. The negative bands increasing with time can be explained by slower rate of dehydration, that is styrene formation, compared to the rate of replacement of styrene by PE on the surface, leading to some depletion of styrene on the surface with increasing time.


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Figure 7. (a) Time-resolved IR spectra of PE (2 mM) adsorption on Pd/SA-15. (b) Timeresolved IR spectra of PE (2 mM) hydrogenation on Pd/SA-15.

Generally, alcohols have the ability to be dehydrated on acidic supports. Strong Lewis acid alumina is a very popular catalyst for gas-phase alcohol dehydration. In the liquid phase, alumina with strong Lewis acidity did not show significant activity in PE dehydration to styrene, whereas Brϕnsted acid sites with medium strength as existing on Pd/SA-15 could efficiently dehydrate PE to styrene. This is corroborated by the phase-domain spectrum of PE adsorption-desorption on Pd/SA-15 (Figure 8a). Styrene was produced from PE on the support of Pd/SA-15. The phase delay is 250º (360º-110º) for the band at 1656 cm-1 assignable to C=C stretching vibration of styrene, whereas PE bands at 1494 cm-1 and 1452 cm-1 show a phase delay of 50º (360º-310º).


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a

b

Figure 8. Phase-domain IR spectra of PE (2 mM) adsorption on (a) Pd/SA-15 and (b) Pd/SA70.

This observation indicates that the dehydration of PE is relatively slow compared to the other reaction steps. Normally, enhancing the acidity can promote the dehydration rate of alcohols. Pd/SA-70 possesses higher support acidity than Pd/SA-15. As shown in Figure 9a, the timeresolved ATR-IR spectrum recorded during PE adsorption also showed a negative going band at 1659 cm-1 assignable to C=C stretching vibration of styrene. Note that the intensity of this band in Figure 9a is far lower than that of the corresponding band at 1656 cm-1 in Figure 7a


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(Pd/SA-15), which can be explained by faster dehydration of PE to styrene on Pd/SA-70 compared to Pd/SA-15.

Figure 9. (a) Time-resolved IR spectra of PE (2 mM) adsorption on Pd/SA-70. (b) Timeresolved IR spectra of PE (2 mM ) hydrogenation on Pd/SA-70.

This could be caused by the favored protonation of styrene on stronger Brϕnsted acid sites, existing on the support of Pd/SA-70, and their propensity to generate hydrocarbon cations23, In Figure 9b, similar as in the hydrogenation on Pd/SA-15 (Figure 7b), the styrene produced via PE dehydration disappeared after introduction of hydrogen and converted to EB. Information about the kinetics of styrene formation on Pd/SA-70 emerges from the phase-domain spectrum shown in Figure 8b, which further confirmed that styrene was produced from PE on Pd/SA-70. The phase delay of the signal at 1656 cm-1 due to the C=C


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stretching vibration of styrene is 230º (360º-130º), whilst it is 30º (360º-330º) for bands of PE (1494 cm-1 and 1452 cm-1). Hence PE adsorption was faster on Pd/SA-70 compared to Pd/SA-15. Styrene production was also faster on Pd/SA-70 (phase-delay of 230º), compared to Pd/SA-15 (phase-delay of 250º). More styrene generated via dehydration resulted in more EB produced during AP hydrogenation. Assuming that PE dehydration on Brϕnsted acid sites is the rate limiting step in the PE hydrogenation, the support acidity has a stronger effect on EB yield and selectivity, than on AP conversion as also emerges from the catalytic results shown in Figure 1 and Table S1. The present study demonstrates how the cooperative action of Brϕnsted acidity of the support required for dehydration and the metal function needed for hydrogenation can significantly enhance the efficiency of the chemoselective hydrogenation of aromatic ketones to related alkyl aromatics. Proper tuning of these catalytic functions provides a powerful tool for improving the efficiency of bifunctional catalysts, where acidic and metallic sites act in concert.

4. CONCLUSIONS The role of acidic surface sites on silica-alumina (SA) supported palladium nanoparticles in the chemoselective hydrogenation of a model aromatic ketone, acetophenone (AP), has been investigated by means of in situ ATR-IR spectroscopy together with MES and PSD. For this purpose Pd nanoparticles supported on SA supports with different aluminum content (0, 15, 70 wt%), resulting in different strength and population of acidic sites were applied. AP hydrogenation showed improved ethyl benzene (EB) selectivity and yield with increasing surface acidity. The modulation–excitation in situ ATR-IR study indicates that the initial AP hydrogenation product, phenyl ethanol (PE), dehydrates on Brϕnsted acidic sites of the silicaalumina supports producing styrene. Subsequently the styrene either desorbs into the liquid


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phase or is further hydrogenated to EB. These findings are in line with a hydrogenationdehydration mechanism, which consists of the hydrogenation of the carbonyl bond of AP to the corresponding alcohol PE, succeeded by its dehydration to styrene and its subsequent hydrogenation of the C=C double bond to EB. Unlike strong Lewis acid alumina in liquid phase hydrogenation, Brϕnsted acid sites still kept their functions for efficient dehydration of PE to styrene, which directed the reaction route to the easier hydrogenation-dehydration mechanism compared to direct hydrogenolysis. On SA supports with higher acidity, PE could not replace AP to promote the reaction during the hydrogenation. However, the increase of surface acidity promotes the PE adsorption on the support and enhances the rate of AP adsorption/desorption on Pd/SA catalysts (the rate of AP adsorption-desorption follows Pd/SA-70 > Pd/SA-15 > Pd/silica). In addition, the higher acidity promoted styrene formation via PE dehydration. The cooperative action of Brϕnsted acidity for dehydration and metal function for hydrogenation on the bifunctional catalysts could significantly enhance the efficiency of the chemoselective hydrogenation of aromatic ketones. ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: acscatal.XXX. Catalyst synthesis; Acidity characterization of catalysts; ATR-IR-MES measurements; Catalytic results of acetophenone (AP) hydrogenation (Table S1); IR spectra of pure liquid AP, PE and EB (Fig. S1-3); Co-adsorption of AP and PE (Fig. S4-6); Adsorption of PE on Pd/silica (Fig. S7). AUTHORS INFORMATION Corresponding Authors * Email: [email protected]


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* Email: [email protected] ORCID

Alfons Baiker: 0000-0003-1408-464X

ACKNOWLEDGMENT We acknowledge the financial supports from Australian Research Council Discovery Projects (DP150103842) and the Faculty’s MCR Scheme, Energy and Materials Clusters, SOAR Fellowship at the University of Sydney.

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