Nb2O5 promoted Pd/AC catalyst for selective phenol hydrogenation to cyclohexanone

Chunhua Zhang,Zhengyan Qu,Hong Jiang,Rizhi Chen,*,Weihong Xing,*

1 State Key Laboratory of Materials-Oriented Chemical Engineering,Nanjing Tech University,Nanjing 210009,China

2 Changzhou Key Laboratory of Eco-Textile Technology,Changzhou Vocational Institute of Textile and Garment,Changzhou 213164,China

Keywords:Phenol hydrogenation Cyclohexanone Nb2O5 Pd/AC Acidity

ABSTRACT Phenol hydrogenation is a green route to prepare cyclohexanone,an intermediate for the production of nylon 66 and nylon 6.The development of high-performance catalysts still keeps a great challenge.Herein,the activated carbon (AC) was modified with an acidic material Nb2O5 to adjust the microstructure and surface properties of AC,and the influences of the calcination temperature and Nb2O5 content on the catalytic performance of the Pd/AC-Nb2O5 catalysts for the phenol hydrogenation to cyclohexanone were investigated.The Nb2O5 with proper content can be highly uniformly distributed on the AC surface,enhancing the acidity of the Pd/AC-Nb2O5 catalysts with comparable specific surface area and Pd dispersion,thereby improving the catalytic activity.The hybrid Pd/AC-10Nb2O5-500 catalyst exhibits the synergistic effect between the Pd nanoparticles and AC-10Nb2O5,which enhances the catalytic activity for the hydrogenation of phenol.Furthermore,the as-prepared Pd/AC-10Nb2O5-500 catalyst shows good reusability during 7 reaction cycles.

1.Introduction

Cyclohexanone is an important organic intermediate in the synthesis of adipic acid and caprolactam,which is further used for the production of nylon 66 and nylon 6 [1–3].In general,cyclohexanone is produced by cyclohexane oxidation or phenol hydrogenation in industry[4,5].Cyclohexane oxidation is usually carried out at high temperature and pressure,leading to high energy cost[6,7].Phenol hydrogenation with relatively low energy consumption and production cost is a more attractive manufacturing method.Therefore,researchers have made significant efforts to develop effective catalysts for selective hydrogenation of phenol to cyclohexanone in recent years [8–10].One of the important ways to increase the hydrogenation activity is the addition of promoters to the catalysts for the controllable design of catalysts,such as alkaline earth metal or rare earth metal [11,12].On the other hand,improving utilization of active components,size-controlling and heightening percentage dispersion of metal nanoparticles also play important roles in the improvement of the catalytic performance [13–15].Hence,developing new types of catalysts containing designed active components and supports is in favor of achieving high phenol conversion and cyclohexanone selectivity.

Carbon materials with numerous fascinating characteristics,such as large specific surface area,good chemical stability and low manufacturing cost,are ideal candidates as catalyst carriers[16–19].Activated carbon(AC),as one of carbon materials,is usually used as the catalyst support [20,21].However,the activated carbon with perfect carbon matrices is proved to be too inert to anchor the active centers,resulting in the aggregation of metal nanoparticles and thereby deactivation of the catalyst[22].Therefore,the development of functional activated carbons and research on the function mechanism are crucial.

Niobium pentaoxide (Nb2O5) with moderate acid property is often used as a functional carrier [23,24].Recently,publications have shown that there is a strong metal-support interaction(SMSI)effect existing in Nb2O5-supported catalysts,which have been widely studied [25–27].In addition,Nb2O5can be dispersed on the surface of the carrier,and plays a role in increasing the anchoring of metal nanoparticles,thereby improving the catalytic activity[28,29].Liuet al.[30]prepared Nb2O5and carbon composite nanofibers(Nb2O5/C),which was applied as the electrochemical support for Pt metal nanoparticles employing in the methanol oxidation reaction (MOR).The as-prepared Pt/Nb2O5/C catalyst demonstrated excellent electrochemical activity toward MOR,which was related to the enhanced electrical conductivity of Nb2O5/C and the strong interaction between the mental particles and Nb2O5doped support.Liuet al.[31] modified the Pt/ZrO2with Nb2O5,which produced some Lewis acid sites and demonstrated higher activity and N2selectivity toward the selective catalytic reduction of NO by H2as compared to Pt/ZrO2.

Considering the great influences of the acid-base property of catalyst supports and reaction conditions on the catalytic activity,efforts have been devoted to improving the catalytic performance of phenol hydrogenation to cyclohexanone.For example,Liuet al.[32] prepared dual supported Pd-Lewis acid catalyst,which showed high phenol conversion (>99.9%) and excellent cyclohexanone selectivity (>99.9%).Moreover,Liet al.[33] tuned the catalytic activity of phenol hydrogenation over Pd/C by using various acids such as HCOOH and CH3COOH including carboxyl group,which demonstrated the different promoting effect.Inspired by these findings,herein we modified the Pd/AC with acidic material Nb2O5for achieving the synergistic effect between the Pd and Nb2O5in the selective phenol hydrogenation to cyclohexanone.The results demonstrate that the addition of Nb2O5significantly improves the acidity of Pd/AC-Nb2O5,leading to a strong interaction between the metal Pd and AC-Nb2O5,thereby increasing the catalytic activity in the phenol hydrogenation to cyclohexanone as compared to the Pd/AC catalyst.Besides,the Pd/AC-Nb2O5catalyst reveals good reusability during 7 recycling experiments as well as Pd/AC.

2.Experimental

2.1.Chemicals

Activated carbon (AC) was brought from Jiangsu Zhuxi Activated Carbon Co.,Ltd.,China.Niobium pentaoxide (Nb2O5) was purchased from Aladdin.Palladium acetate (Pd(OAc)2) was provided by Sin-platinum Metals Co.,Ltd.,China.Acetone(CH3COCH3)was obtained from Shanghai Lingfeng Chemical Regent Co.,Ltd.,China.Phenol (C6H5OH) was purchased from Sinopharm Chemical Reagent Co.,Ltd.,China.Cyclohexane (C6H12) was purchased from Shanghai Shenbo Chemical Regent Co.,Ltd.,China.All the chemicals were used as received without purification.

2.2.Catalyst preparation

The synthesis of the Pd/AC-Nb2O5catalyst was illustrated in Fig.1.

2.2.1.Synthesis of Nb2O5 doped AC supports

Fig.1.Schematic diagram of the Pd/AC-Nb2O5 preparation.

AC supports with different Nb2O5loadings were obtained by an impregnation method.A certain quality of Nb2O5was uniformly dispersed in 20 ml of deionized water with stirring for 10 min,and then 2 g of AC was added with continuous magnetic stirring(24 h).Then,the deionized water was removed from the mixed solution through rotary evaporation.After that,the black residues were dried in an oven at 70 °C overnight.The obtained samples were calcined in a tube furnace under argon atmosphere at a certain temperature for 3 h with a heating rate of 10 °C?min-1.The samples were denoted as AC-xNb2O5-y,wherexrepresents the weight percent of Nb2O5andyrepresents the calcination temperature.

2.2.2.Preparation of the Pd/AC-Nb2O5 catalysts

The Pd/AC-Nb2O5catalysts were prepared by an impregnation method using Pd(OAc)2as the precursor.1 g of AC-Nb2O5and 0.043 g of Pd(OAc)2were added into 25 ml of acetone and stirred at 30°C for 12 h.Then,the obtained mixture was put into a rotary evaporator to remove the acetone and finally was dried in an oven at 70 °C overnight.

2.2.3.Synthesis of the Pd/AC and Pd/AC+Nb2O5 catalysts

For comparison,Pd/AC-0Nb2O5-500 (Pd/AC) was prepared by the above method.Nb2O5(0.2 g)was placed in the deionized water with stirring for 10 min,then the as-prepared Pd/AC (1.8 g) was added with continuous stirring.The obtained mixture was then submitted to rotary evaporation and dried as described above.The resultant catalyst was labeled as Pd/AC+Nb2O5.

2.3.Catalyst characterization

Powder X-ray diffraction(XRD)analysis was carried on Miniflex 600 with Cu Kα radiation.NH3temperature-programmed desorption(NH3-TPD)was conducted on an Auto Chem 2920 equipment.The textural properties of the as-synthesized catalysts were determined by N2adsorption/desorption on a Micromeritics ASAP 2020 apparatus.The surface morphology and microstructure were characterized by field emission scanning electron microscopy (FESEM,Hitachi S-4800) and transmission electron microscopy (TEM,JEOL JEM-2100).The Pd contents were determined by the inductively coupled plasma emission spectroscopy (ICP-AES,Optima 7000DV).The X-ray photoelectron spectroscopy (XPS) measurement was taken to investigate the elemental analysis of the asprepared catalysts using a Thermo ESCALAB 250Xi apparatus with monochromatized Al Ka radiation at 1486.6 eV.The dispersion of Pd nanoparticles was evaluated by CO pulse chemisorption on an Auto Chem 2920 apparatus.

2.4.Catalytic tests

Catalytic tests for phenol hydrogenation to cyclohexanone were conducted in a stainless steel reactor at a stirring speed of 100 r?min-1for 20 min.The typical reaction conditions were as follows:80°C,5 ml of 1%(mass)phenol-cyclohexane solution,0.1 g of catalyst,and 0.1 MPa of H2pressure.Before the catalytic reaction,0.2 MPa H2was purged into the sealed autoclave reactor to drive away air for 5 times.After reaction,the autoclave reactor was cooled to room temperature.The products were quantitatively analyzed using the internal standard method by gas chromatrography(GC-2014)with a PEG-20 M capillary column and a FID detector [34].Trimethylbenzene was used as an internal standard.According to the GC analyses,the numbers of carbon atoms in the reactant phenol were almost the same as those in the products cyclohexanone and cyclohexanol,and carbon balances for all cases were close to 100%.

3.Results and Discussion

3.1.Microstructure properties of the catalysts

The crystalline structures of the as-prepared catalysts were studied using XRD,as shown in Fig.2.For Pd/AC,a broad diffraction peak is located at 23°,which is related to AC [35].In contrast,Nb2O5shows many obvious diffraction peaks corresponding to the phases of orthorhombic and monoclinic[36–39].The Nb2O5crystal phases with orthorhombic and monoclinic structures are detected in all the Nb2O5doped catalysts.With increasing the Nb2O5doping,its diffraction peaks become sharp(Fig.2(d)).The phenomena indicate that Nb2O5is successfully doped in the Pd/AC-Nb2O5and Pd/AC+Nb2O5catalysts.Besides,it can be seen that the calcination of AC-Nb2O5at 500°C has no obvious effect on the Nb2O5crystalline structure.It is worth mentioning that Pd diffraction peaks are not detected in the XRD patterns,which is most likely because of the high Pd dispersion on the carriers [29].

The textural properties of the as-prepared catalysts were tested by nitrogen adsorption–desorption measurements.Similar N2adsorption–desorption isotherms (Type I/IV) are obtained for all catalysts (Fig.3),suggesting the characteristics of microporous and mesoporous[40,41].Doping Nb2O5causes a gradual reduction of surface area from 1190(Pd/AC)to 920 m2?g-1(Pd/AC-20Nb2O5-500) (Table 1).The specific surface areas of mesopores and micropores decrease simultaneously.The phenomena might be due to the presence of Nb2O5,which might block the pores to some extent.The pore volume exhibits the similar change trend.Compared to Pd/AC,no significant changes of surface area and pore volume are observed for the Pd/AC+Nb2O5catalyst prepared by physically mixing,which may be due to the very small specific surface area of Nb2O5(3 m2?g-1).This result is consistent with the phenomenon discovered by Xionget al.[42].

Fig.4 gives the NH3-TPD results of the as-prepared catalysts.It can be seen that four catalysts all show NH3desorption peaks at temperatures higher than 200 °C.For the four Pd/AC catalysts,the maximum desorption temperature follows the order:Pd/AC-10Nb2O5-500 (267 °C) >Pd/AC-20Nb2O5-500 (263 °C) >Pd/AC +Nb2O5(261 °C) >Pd/AC (259 °C).In contrast,no obvious NH3desorption peaks are observed for Nb2O5,which is consistent with that reported by Yeet al.[29].That may be the reason for no significant changes of the NH3desorption peaks for the catalysts with the Nb2O5doping.It is well known that the acidic strength can be revealed by the maximum desorption temperature of NH3.Obviously,Pd/AC-10Nb2O5-500 shows higher maximum desorption temperature than Pd/AC-20Nb2O5-500 as reported by Guan and coworkers [29].This means that the acidic strength first increases and then decreases with the increase of Nb2O5loading,possibly because the dispersion of Nb2O5becomes worse at higher loading.And the acidity of Nb2O5is mainly ascribed to both Lewis acid sites and Bronsted acid sites on its surface [43].These results highlight that the doping of Nb2O5,especially the in-situ doping,can enhance the acidity of the Pd/AC catalysts.

Fig.2.XRD patterns of (a) Nb2O5,(b) Pd/AC,(c) Pd/AC-10Nb2O5-500,(d) Pd/AC-20Nb2O5-500,(e) Pd/AC+Nb2O5.

Fig.3.Nitrogen adsorption–desorption isotherms of(a)Pd/AC,(b)Pd/AC-10Nb2O5-500,(c) Pd/AC-20Nb2O5-500,(d) Pd/AC+Nb2O5.Solid symbols indicate gas absorption and open symbols express gas desorption.

From the CO chemisorption(Table 2),it is seen that the Pd dispersion is 29.5% for Pd/AC and 29.9% for the physically mixed catalyst Pd/AC+Nb2O5.Compared to the Pd/AC and Pd/AC+Nb2O5catalysts,the as-fabricated Pd/AC-10Nb2O5-500 and Pd/AC-20Nb2O5-500 catalysts show lower Pd dispersion,decreasing to 28.4% and 24.7%,respectively.The results indicate that modifying the activated carbon with Nb2O5is unfavorable for the Pd dispersion,and the phenomenon is consistent with the result observed by Liuet al.[31].The reason may be the reduction of surface area derived from loading Nb2O5(Fig.3,Table 1).Correspondingly,the particle size of Pd nanoparticles also increases(Table 2).However,the particle sizes of Pd in the four catalysts are all maintained in the range of nanometer.

The XPS analysis was performed to determine the surface chemical composition of the catalysts.The results in Fig.5(a) and Table 3 indicate that C,N,O and Pd are the main elements on the surfaces of four catalysts.Besides,Nb element is also detected in the Nb2O5doped catalysts,which increases with increasing the Nb2O5doping as expected.It is worth mentioning that the surface Pd content increases from 0.19% (Pd/AC) to 0.26% for Pd/AC-10Nb2O5-500 and 0.29%for Pd/AC-20Nb2O5-500.At the same time,the surface Pd content in Pd/AC+Nb2O5is similar to that in Pd/AC.The results clearly show that the doping of Nb2O5leads to a significant increase in the surface Pd content,possibly because of the decreased surface area (Fig.3,Table 1) and/or the strong interaction between Pd nanoparticles and AC-Nb2O5carriers [30].The higher content of surface Pd is convenient for the contact between the reactants and active centers,thereby improving the catalytic activity.

Table 1 Textural properties of various catalysts

Table 2 Pd content,dispersion and particle size of the catalysts

To verify the forms of Pd and Nb elements,the XPS spectra of Pd 3d and Nb 3d were decomposed.Pd 3d spectra of all samples can be decomposed into two peaks (Fig.S1),which are related to the Pd 3d5/2(337.6 eV) and Pd 3d3/2(343.0 eV) of Pd (2+) species[44].The peaks of Nb 3d spectra of Pd/AC-20Nb2O5-500 and Pd/AC+Nb2O5are located at 207.7 and 210.4 eV (Fig.5(c) and (d)),which are ascribed to the Nb 3d5/2and Nb 3d3/2of Nb (5+) oxidation state presented in Nb2O5[45].However,the Nb 3d spectra of Pd/AC-10Nb2O5-500 exhibit two peaks with binding energies at 208.3 and 211.0 eV (Fig.5(b)).Clearly,the binding energy of Nb 3d for the Pd/AC-10Nb2O5-500 catalyst positively shifts to higher energy as compared to the Pd/AC-20Nb2O5-500 and Pd/AC+Nb2O5catalysts.The positive change in the binding energies of Nb 3d could be attributed to the uniform dispersion of niobium on the AC support,as discussed in the following TEM characterization(Fig.6),which is also in favor of the generation of a surface acidity and the formation of a strong interaction between the Pd and AC-10Nb2O5-500 [46].The findings are consistent with characterization results of NH3-TPD (Fig.4).

Fig.4.NH3-TPD profiles of(a)Nb2O5,(b)Pd/AC,(c)Pd/AC-10Nb2O5-500,(d)Pd/AC-20Nb2O5-500,(e) Pd/AC+Nb2O5.

In order to analyze the surface morphology and microstructure of the as-prepared samples,FESEM and TEM images were taken.From the FESEM analysis (Fig.S2),there is no apparent difference in the four catalysts,and all catalysts exhibit irregular morphologies.The findings are similar to the report in the literature [47].The AC-10Nb2O5-500 support as a typical sample was characterized by TEM (Fig.6).The Nb2O5on AC exhibits high crystallinity with a lattice spacing of 0.39 nm (Fig.6(b)),which is related to the(0 0 1)plane of Nb2O5[48].The finding further testifies the successful doping of Nb2O5,in accordance with the XRD (Fig.2) and XPS(Fig.5,Table 3)analyses.Notably,the Nb2O5can be uniformly distributed on the AC-10Nb2O5-500 support (Fig.6(b)),promoting the positive shift of the binding energy of Nb 3d (Fig.5).

3.2.Catalytic performance and recyclability of Pd/AC and Pd/AC-Nb2O5

Fig.7 exhibits the catalytic performance of the as-fabricated catalysts in terms of phenol conversion and selectivity to cyclohexanone.The Pd(2+)species in the fresh catalysts(Fig.S1)can beinsitureduced to metal Pd nanoparticles during the reaction,promoting the phenol hydrogenation to cyclohexanone[49].Considering that the calcination temperature probably influences the catalytic performance of Pd/AC-Nb2O5,AC-10Nb2O5was used as a carrier for preparing the Pd/AC-10Nb2O5catalysts to investigate the effect of the calcination temperature on the catalytic performance.As illustrated in Fig.7(a),the cyclohexanone selectivity for each catalyst is higher than 96%,because the existence of N element in the catalysts(Table 3)is in favor of the formation of cyclohexanone [50].The result suggests that the calcination temperature has no obvious influence on the cyclohexanone selectivity.It is clearly seen that with the increase of calcination temperature,the phenol conversion first increases and then decreases,and Pd/AC-10Nb2O5-500 has the highest catalytic activity.The lower catalytic activity of Pd/AC-10Nb2O5-400 may be ascribed to its lower acidity [29].Higher calcination temperature may reduce the acid density,leading to lower catalytic activities of Pd/AC-10Nb2O5-600 and Pd/AC-10Nb2O5-700[29].These results demonstrate that the proper acidity of Pd/AC contributes to better catalytic activity in the phenol hydrogenation to cyclohexanone,and 500 °C is a feasible calcination temperature for the doping of Nb2O5and the preparation of Pd/AC-Nb2O5.

The doping content of Nb2O5should be an important factor that affects the catalytic performance of Pd/AC-Nb2O5.Therefore,the influence of the doping content of Nb2O5on the catalytic performance of Pd/AC-Nb2O5-500 was investigated (Fig.7(b)).Similarly,the doping content of Nb2O5also has no significant effect on the cyclohexanone selectivity.As can be seen,the phenol conversion increases with increasing the doping content of Nb2O5.Nb2O5as Lewis acid can further polarize the benzene ring in phenol and thus enhance the reaction activity [33].Particularly,when the doping content increases to 10%,the phenol conversion of Pd/AC-10Nb2O5-500 reaches the maximum.Further increasing the doping content to 15% and 20%,the phenol conversion shows a decline trend due to the reduction of specific surface area (Fig.3,Table 1),Pd dispersion(Table 2)and acidity(Fig.4).The results indicate that 10%is a feasible doping content of Nb2O5for fabricating the Pd/ACNb2O5catalyst.

Table 3 Atomic concentration of elements in the catalysts

Fig.5.XPS survey spectra of four different Pd/AC catalysts (a),Nb 3d spectra of Pd/AC-10Nb2O5-500 (b),Pd/AC-20Nb2O5-500 (c),Pd/AC+Nb2O5 (d).

To further investigate the contributions of the Nb2O5and Pd on the hydrogenation activity of Pd/AC-Nb2O5,the catalytic performances of the support AC-10Nb2O5-500 and physically mixed catalyst Pd/AC+Nb2O5were also evaluated and compared.For AC-10Nb2O5-500,no reaction takes place.With respect to Pd/AC+Nb2-O5,the phenol conversion and cyclohexanone selectivity are 61.4%and 96.1%,respectively.For Pd/AC,the phenol conversion and cyclohexanone selectivity are 63.1% and 96.6% (Fig.7(b)),respectively.The lower phenol conversion of Pd/AC+Nb2O5in comparison with Pd/AC should be caused by the lower Pd loading.As presented in the Experimental Section,the Pd/AC+Nb2O5catalyst with a Nb2O5content of 10% (mass) was prepared by physically mixing of the as-prepared Pd/AC and Nb2O5.As a result,Pd/AC+Nb2O5has lower Pd loading as compared to Pd/AC (Table 2).In this study,the same amount of catalyst (0.1 g) was used in all tests.Thus,for Pd/AC+Nb2O5,few amount of Pd was used in the reaction,resulting in the lower phenol conversion.For eliminating the effect of Pd loading,the turnover frequency (TOF) was calculated.The results show that Pd/AC+Nb2O5almost has the same TOF value (53.8 h-1) as Pd/AC (53.0 h-1),indicating the same catalytic activity of Pd/AC+Nb2O5as Pd/AC.However,at the similar Pd loading (Table 2),Pd/AC-10Nb2O5-500 has significantly higher phenol conversion as compared to Pd/AC,suggesting the higher catalytic activity of Pd/AC-10Nb2O5-500.The results indicate that Pd is the active center for the selective hydrogenation of phenol to cyclohexanone,and thein-situdoping Nb2O5on the AC surface can improve the catalytic activity of Pd/AC.Together with the aforementioned characterizations,it can be concluded that the Nb2O5with proper content can be highly uniformly distributed on the AC surface (Figs.5 and 6(b)),enhancing the acidity of the Pd/AC-Nb2O5catalysts (Fig.4) with comparable specific surface area (Table 1) and Pd dispersion (Table 2),thereby improving the catalytic activity (Fig.7(b)).The hybrid Pd/AC-10Nb2O5-500 catalyst exhibits the synergistic effect between the Pd nanoparticles and AC-10Nb2O5,which enhances the catalytic activity for the hydrogenation of phenol.

Fig.6.TEM image (a) and high resolution TEM image (b) of AC-10Nb2O5-500.

Fig.7.Catalytic performance of Pd/AC-Nb2O5 catalysts with different synthesis parameters for the selective hydrogenation of phenol:(a) Calcination temperature,(b)Content of Nb2O5.

The catalytic stability of a catalyst is a key to evaluate its practical application.Given the excellent performance of Pd/AC-10Nb2O5-500 in the phenol hydrogenation,it was selected for the stability test (Fig.8).For comparison,the catalytic stability of Pd/AC was also evaluated.It can be clearly seen that both Pd/AC-10Nb2O5-500 and Pd/AC catalysts show stable catalytic performance in the 7 runs.Compared with the XRD patterns (Fig.2)and FESEM images (Fig.S2) of the fresh ones,there is no obvious change in the XRD (Fig.S3) and FESEM (Fig.S4) results of the recovered Pd/AC-10Nb2O5-500 and Pd/AC catalysts.This means that the crystal structure and surface morphology of the two catalysts keep stable during the 7 runs.The results demonstrate that the as-prepared Pd/AC-10Nb2O5-500 catalyst has good catalytic performance in the selective hydrogenation of phenol to cyclohexanone.

Fig.8.Stability tests of the Pd/AC and Pd/AC-10Nb2O5-500 catalysts.

4.Conclusions

A serial of Pd/AC-Nb2O5catalysts were fabricated by the modification of AC with the Nb2O5doping and then the loading of Pd nanoparticles,and their catalytic performances were evaluated in the selective phenol hydrogenation to cyclohexanone.The calcination temperature and Nb2O5content significantly affect the phenol conversion,while have no obvious influence on the cyclohexanone selectivity.The doping of Nb2O5as Lewis acid enhances the acidity of the Pd/AC catalysts,which can accelerate the polarization of benzene ring in phenol,thereby increasing the reaction activity.The as-fabricated Pd/AC-10Nb2O5-500 catalyst exhibits superior catalytic activity as compared to the AC-10Nb2O5-500,Pd/AC and physically mixed catalyst Pd/AC+Nb2O5,indicating the synergistic effect between the Pd nanoparticles and AC-10Nb2O5.The studies provide insights into the synthesis of the catalysts with highperformance for the phenol hydrogenation to cyclohexanone.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The financial supports from the National Natural Science Foundation (21776127,21921006),the Jiangsu Province Key R&D Program (BE2018009-2),the Jiangsu Province natural science research of College and university general project (20KJB540003),a project funded by the priority academic program development of Jiangsu higher education institutions(PAPD),the State Key Laboratory of Materials-Oriented Chemical Engineering (ZK201902),and the outstanding young teacher’s project of Changzhou Vocational Institute of Textile and Garment of China are gratefully acknowledged.

Supplementary Material

Supplementary data to this article can be found online at https://doi.org/10.1016/j.cjche.2021.04.038.