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Article

Synthesis of Tetrahydropyran from Tetrahydrofurfuryl Alcohol over Cu–Zno/Al2O3 under a Gaseous-Phase Condition

by
Fengyuan Zhang
1,2,3,
Bin Zhang
4,
Xincheng Wang
1,2,
Long Huang
1,2,*,
Dekun Ji
1,2,
Songsong Du
1,3,
Lei Ma
1,2 and
Shijing Lin
1,2
1
College of Chemical Engineering, Beijing Institute of Petrochemical Technology, Beijing 102617, China
2
Beijing Key Laboratory of Fuels Cleaning and Advanced Catalytic Emission Reduction Technology, Beijing 102617, China
3
Graduate School of Beijing University of Chemical Technology, Beijing 100029, China
4
Institute of Coal Chemistry, Chinese Academy of Sciences, P.O. Box 165, Taiyuan 030001, China
*
Author to whom correspondence should be addressed.
Catalysts 2018, 8(3), 105; https://doi.org/10.3390/catal8030105
Submission received: 24 January 2018 / Revised: 7 February 2018 / Accepted: 7 February 2018 / Published: 6 March 2018
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Versions Notes

Abstract

:
Tetrahydropyran (THP) represents an O-containing hetero-cyclic compound that can be used as a promising solvent or monomer for polymer synthesis. In this work, Cu–ZnO/Al2O3 catalysts have been prepared by a facile precipitation–extrusion method and used for the synthesis of THP through gaseous-phase hydrogenolysis of tetrahydrofurfuryl alcohol (THFA). The effect of the molar ratio of Cu/Zn/Al, reaction temperature, and hydrogen pressure was investigated. An 89.4% selectivity of THP was achieved at 270 °C and 1.0 MPa H2. Meanwhile, the optimum molar ratio of Cu/Zn/Al was determined to be 4:1:10. The Cu–ZnO/Al2O3 catalyst exhibited high catalytic activity and stability for 205 h on-stream. A possible reaction mechanism involving several consecutive reactions was proposed: THFA was firstly rearranged to 2-hydroxytetrahydropyran (2-HTHP), followed by the dehydration of 2-HTHP to 3,4-2H-dihydropyran (DHP) over acid sites; finally, the DHP was hydrogenated to THP. The synergy of acid sites and metal sites of Cu–ZnO/Al2O3 played an important role during the production of THP.

1. Introduction

Catalytic upgrading of biomass-derived furfural or its derivatives to value-added chemicals has received great attention in recent years [1,2,3]. Furfural and 5-hydroxymethylfurfural (HMF), which are considered to be promising biorenewable platform chemicals, can be derived through acid-catalyzed dehydration of hemicellulose from various abundant agricultural raw materials, such as hemicellulose grain shell, hardwood lumber, corncobs, wheatbran, and other renewable biomass materials [4,5,6,7]. There were intense studies carried out on the production of high value-added chemical intermediates and end products from HMF using heterogeneous catalysts [8,9,10,11]. Tetrahyrofurfuryl alcohol (THFA) can be obtained through hydrogenation of furfural at a very high yield [12], and from which various useful chemicals, such as 1,5-pentadiol (15PDO) [13,14,15,16,17,18,19,20,21,22,23,24,25], 3,4-2H-dihydropyran (DHP) [26,27,28], and 4-penten-1-ol can be produced [29,30]. 15PDO, via a ring closure pathway, can form tetrahydropyran (THP) through the participation of strong solid acid catalysts or high-temperature water [31]. Moreover, THP can be obtained by the hydrogenation of DHP [32]. THP can be used as both a solvent and an intermediate in the synthesis of organic compounds such as glutaric acid, heptanediamine, 1,5-dichloropentane, and pimelic acid [32,33]. However, the synthesis of THP directly from THFA using heterogeneous catalysts is rarely reported.
Recently, the catalytic conversion of furanics has been extensively studied over noble metal catalysts. However, due to the high cost and depleting resources of noble metals, it is of great importance to explore catalytic systems over non-noble metals. Among non-noble metals, copper-based catalysts were widely used in hydrogenation and hydrogenolysis reactions due to their good catalytic performance and low cost. Müller et al. [34] found that dimethyl succinate could be completely converted to THF over CuO–ZnO/Al2O3 at 220/Allely MPa. Guo et al. [35] also reported that a selectivity of THF as high as 94% could be obtained over Cu-B/Al2O3 during the hydrogenolysis of dimethylsuccinate. The selective conversion of furanic-derived compounds over Cu catalysts is particularly encouraging and needs further investigation. Soghrati et al. [36] reported that a 70% yield of THP was achieved via hydrogenolysis of THFA over Ni/HZSM-5 catalyst, encouraging us to investigate the probability of producing THP from THFA over Cu catalysts.
In this paper, we have prepared a bi-functional Cu–ZnO/Al2O3 catalyst by a facile precipitation extrusion method. The physic-chemical properties were characterized by XRD, BET, TEM, NH3-TPD, and H2-TPR analysis. The role of Cu metal sites during the direct conversion of THFA to THP over Cu–ZnO/Al2O3 catalysts was studied. The effect of temperature, pressure, and catalysts on THFA to THP along with side reactions was investigated. The current work was beneficial to develop the downstreams of TFHA over non-noble catalysts.

2. Results and Discussion

2.1. Catalyst Characterization

2.1.1. BET Characterization

The porosity and pore-size distribution of the calcined Cu–ZnO/Al2O3 extrudate catalysts were determined by N2 adsorption–desorption. The γ-Al2O3 (boehmite particles behaving as a binder and supplying acid sites) exhibited a 12 nm mean diameter (Figure S1). Accordingly, the volume-size distribution of Cu–Zn particles was characterized as a bimodal distribution with a mean diameter of 2.7 nm. The other peak resulting from 8.2 nm particles was possibly derived from symbiotic fragments. Therefore, the extrudate’s pore size distribution might be related with the solid composition, because the respective catalysts particle sizes differed significantly; therefore, the effect of the amount of γ-Al2O3 on the main peak of the size distribution was not negligible. Lamelleted mesoporous materials exhibited a typical type-III shaped isotherm, obtained by nitrogen adsorption–desorption measurements (Figure S2). The surface areas (SBET) of the calcined catalysts increased monotonically from 196.4 to 261.7 m2·g−1 with the increase in the content of γ-Al2O3, though they were generally lower than that of γ-Al2O3 (A0-0-01) (Table 1). This is consistent with the study by Kraushaar-Czarnetzki et al. [34].

2.1.2. XRD Characterization

The XRD patterns of calcined catalysts are shown in Figure 1. Diffuse diffraction peaks at 2θ = 35.5°, 38.9°, and 64.2° (JCPDS 05-0661) were attributed to crystalline CuO, and the XRD patterns were associated with the copper crystalline size and the copper species [37]. The peak intensities of both CuO and ZnO were weakened with the increase in aluminum content, possibly due to the increased dispersion of Cu and Zn species after the addition of γ-Al2O3 (Figure 2). The copper crystallite size of all catalysts were determined to be 34.4 nm, 26.6 nm, 25.8 nm, 25.0 nm, 24.3 nm, and 22.3 nm by the Scherrer equation, based on the full width at maximum Cu diffraction of 35.5°. The peak of γ-Al2O3 was not observed due to the high dispersion of γ-Al2O3 species.

2.1.3. NH3-TPD Characterization

The acidity of samples was determined by NH3-TPD. The acid distribution was obtained by Gaussian fitting of NH3-TPD curves (Table 2 and Figure S3). Three peaks centered at 104 °C, 225 °C, and 335 °C were fitted for the NH3-TPD curve, attributing to the NH3 desorption from the weak, medium, and strong acid sites, respectively [38]. The total acid sites of γ-Al2O3 (A0-0-01) (7.2 μmol·g−1) was more than three times that of Cu–ZnO. Moreover, a ratio of strong acid sites of A0-0-01, larger than that of Cu–ZnO, was also obtained. When γ-Al2O3 was mixed with Cu–ZnO, the total acid sites increased along with the formation of more medium acid sites, while the ratio of strong acid sites kept relatively constant. The generation of medium acid sites may be due to the interaction between Cu–ZnO and γ-Al2O3 during the preparation process. The amount of strong acid sites increased with the increase in γ-Al2O3, in good agreement with previous reports [39].

2.1.4. H2-TPR Characterization

Figure 2 shows the H2-TPR profile of the calcined catalysts, and an asymmetrical peak can be observed. Generally, the reduction temperature of copper species changes with particle size, chemical environment, and the metal support interaction of Cu oxide species [40,41]. The intensity of reduction peak was reduced with the increased addition of γ-Al2O3 due to the decrease in Cu content. However, the peak area of A4-1-10 is higher than that of A4-1-07, although the Cu content in A4-1-10 is lower, possibly due to the hydrogen spillover. The main reduction peak shifted from 286 °C for A4-1-03 to 268 °C for A4-1-07, indicating an increase in copper oxide dispersion due to the interaction between Cu–ZnO and γ-Al2O3. However, a further increase in the content of γ-Al2O3 resulted in a reduction peak at 285 °C for A4-1-10. Evidently, the change in the H2-TPR peak position indicated the strength of interaction (Cu–ZnO and γ-Al2O3), suggesting that γ-Al2O3 had a great impact on the copper oxide reduction. Moreover, when γ-Al2O3 was added to different catalysts, the reduction process of catalysts became difficult and slower. This resulted from smaller copper oxide particles or the better copper oxide dispersion on the γ-Al2O3 surface.

2.1.5. HRTEM Characterization

To confirm the dispersion and morphology of catalysts particles, HRTEM images of reduced samples (A4-1-00, A4-1-10) were obtained (Figure 3). The dispersion of copper zinc nanoparticles was lower than that of the copper zinc aluminum catalyst. In addition, the Cu particles with sizes <30 nm were observed in the image of the copper zinc aluminum catalyst. Therefore, XRD and HRTEM results are in good agreement with each other.

2.2. Catalysts Performance

2.2.1. Effect of Cu/Zn/Al Ratio

The catalytic performances of the bi-functional Cu–ZnO/Al2O3 catalysts are summarized in Table 3. During the catalytic conversion of THFA, reactions such as rearrangement and hydrogenation could occur, leading to the formation of DHP and THP, respectively. However, DVL and 1-pentanol represent the main by-products during the conversion of THFA, as is shown in Table 3, indicating the existence of strong acid sites. Both A4-1-00 and A0-0-01 showed a low conversion of THFA. The main two products over A4-1-00 were 3,4-2H-dihydropyran (DHP) (Sel. 34.5%) and THP (Sel. 31.3%) at 255 °C and 0.6 MPa H2, suggesting that Cu–ZnO could provide active sites for the rearrangement of THFA and further hydrogenation. In contrast, the main product was DHP over A0-0-01 with 74.4% selectivity, indicating that the γ-Al2O3 could only provide acid sites for THFA rearrangement. For the Cu–ZnO/Al2O3 catalysts, a significant increase in THFA conversion and THP selectivity was observed compared with Cu–ZnO. Furthermore, the conversion of THFA was increased from 11.5 to 78.6%, while the selectivity of THP was improved from 31.3 to 77.8%, when the γ-Al2O3 content increased from A4-1-00 to A4-1-10. However, a further increase in alumina resulted in a decreased THFA conversion (57.4%) and THP selectivity (63.6%).
NH3-TPD results suggested that γ-Al2O3 provided more middle and strong acid sites than Cu–ZnO. These acid sites promoted the rearrangement of THFA to DHP, and DHP can be further converted to THP at hydrogenation sites. However, δ-valerolactone (DVL) was observed as the main byproduct over both γ-Al2O3 and Cu–ZnO/Al2O3 catalysts, while Cu–ZnO with a low content of strong acid sites showed a low selectivity of DVL. Therefore, the formation of DVL may be due to the strong acid sites. The selectivity of THP changed with the Al2O3 content in Cu–ZnO/Al2O3. Thus, the synergy between γ-Al2O3 (acid sites) and Cu–ZnO (metal hydrogenation sites) is the key for a high yield of THP.
In order to investigate the effects of γ-Al2O3 and Cu–ZnO, we compared the catalytic performance of Cu–ZnO/Al2O3 prepared via physical mixing and extrusion. As shown in Table 4, the THP selectivity over Cu–ZnO/Al2O3 prepared via extrusion was lower than that over Cu–ZnO/Al2O3 prepared via physical mixing at 260 °C, 0.6 MPa. However, the THP selectivity over Cu–ZnO/Al2O3 prepared via extrusion was obviously higher than that over Cu–ZnO/Al2O3 prepared via physical mixing at 280 °C, 0.6 MPa. Since the interaction between Cu–ZnO and γ-Al2O3 after extrusion is stronger than that after physical mixing when the temperature was higher, a strong and close interaction between hydrogenation sites (Cu–ZnO) and acid sites (γ-Al2O3) favored the generation of THP from THFA. Therefore, the active sites of hydrogenation and hydrogenolysis reactions were provided by metallic copper, ZnO was used as the adsorbent for THFA reaction, and the acid sites were provided by γ-Al2O3.

2.2.2. Effect of Reaction Temperature and H2 Pressure

The catalytic performance of the A4-1-10 catalyst for THFA conversion at different reaction temperatures (0.6 MPa H2) is shown in Table 5. At a low temperature (230 °C), the selectivity for THP was 55.2%, and the main by-product was DVL. When the reaction temperature increased from 230 to 270 °C, the selectivity of THP increased rapidly from 55.2 to 91.4%. However, the selectivity of THP decreased to 85.9% after further increasing the temperature to 290 °C, due to the intensive formation of 1-pentanol. Generally, 1-pentanol was generated from excessive hydrogenolysis of THFA via the acid-catalyzed ring-opening of THP coupled with metal-catalyzed hydrogenation [42].
Table 6 shows the effect of hydrogen pressure on the activity and selectivity in THFA hydrogenolysis over the A4-1-10 catalyst. At low pressure (<0.4 MPa), the main by-product is DVL. When the pressure increased from 0.2 to 0.8 MPa, THFA conversion increased, while the selectivity of THP increased from 45.5 to 90.5%. On the contrary, the DVL selectivity decreased from 17.7 to 2.6%. The changes in selectivity for THP and DVL indicated that formations of these compounds were competitive reactions. The high pressure of hydrogen promoted the generation of THP by accelerating the hydrogenation of DHP; in the meantime, the dehydrogenation of 2-HTHP was suppressed.
As shown in Figure 4, the Cu–ZnO/Al2O3 catalyst exhibited high activity and stability during 205 h on-stream at 270 °C and 1.0 MPa H2. The THFA conversion and THP selectivity were 99.7% and 89.4%, respectively, after 205 h. Moreover, polymeric materials were not observed in the catalyst bed or colder parts of the unit after the stability test, suggesting that the deposit of polyesters was suppressed over the Cu–ZnO/Al2O3 catalyst.

2.2.3. Reaction Paths

Scheme 1 summarizes the proposed reaction paths during the conversion of THFA to THP over Cu–ZnO/Al2O3, which was in good agreement with prior reports. Sato and coworkers [28] reported that the THFA could be rearranged into 2-hydroxytetrahydropyran (2-HTHP), which was then dehydrated to DHP over acid sites. In the current reaction, DHP was further converted to THP via a C=C bond hydrogenation. The effect of γ-Al2O3 suggested that a close interaction of metal sites and medium acid sites promoted the conversion of THFA to THP. Major by-products, such as DVL and 1-pentanol, were formed through the dehydrogenation of 2-HTHP and over-hydrogenation of THP, respectively. 1-Pentanol was generated at high temperature, and DVL was generated at low temperature and pressure. Therefore, a proper control on both temperature and pressure is needed for the suppressing of byproducts.

3. Experimental

3.1. Catalyst Preparation

The Cu–ZnO/Al2O3 catalysts were prepared by means of the precipitation–extrusion method [34]. γ-Al2O3 produced from boehmite (>400 mesh and 26% m/m water, Shandong Aluminum Corp., Zibo, China), Cu(NO3)2·3H2O (Sinopharm Chemical Reagent Co., Ltd., Shanghai, China), and Zn(NO3)2·6H2O (purchased from Sinopharm Chemical Reagent Co., Ltd., Shanghai, China) were dissolved in water with a final total metal concentration of 1.4 M. Aqueous Na2CO3 (0.3 M) was used as a precipitating agent. During the synthesis procedure, the Na2CO3 solution was added dropwise to a mixed solution of Cu2+ and Zn2+ under vigorous stirring at 70 °C, and the pH was adjusted to 7.0. The resulting precipitate was then aged for 3 h at 80 °C and cooled down to room temperature. The copper/zinc carbonate precursor was obtained after filtration, washing with water for several times, and drying at 120 °C for 4 h.
Before extrusion, the boehmite was mixed with the previously prepared dried copper/zinc carbonate precursor in an Rheo-kneader at room temperature and the rotation speed was kept at 100 r·min−1. The Cu/Zn/Al molar ratio (for instance, 0:0:10, 4:1:00, 4:1:03, 4:1:05, 4:1:07, 4:1:10, and 4:1:15) was modulated by changing the proportion of metal carbonates and boehmite. Herein, the Cu–ZnO/Al2O3 catalyst with a molar ratio of a:b:c is abbreviated as Aabc. For example, the catalyst name of “A4-1-10” means that the molar ratio of CuO/ZnO/Al2O3 was 4:1:10. The paste was then submitted to a piston extruder, and cylindrical green strips with diameters of 3 mm were formed. The green strips were dried at 120 °C for 4 h before calcination at 450 °C for 5 h with a heating rate of 5 °C·min−1.

3.2. Catalytic Reaction

The catalytic performance of the catalysts was investigated in a fixed-bed reactor (i.d. 20 mm, length 300 mm). The catalysts were used in cylinder state with a particle size of 3 mm in diameter. Before reaction, the calcined catalysts were reduced at 275 °C in a 20 vol % H2/N2 atmosphere at a flow rate of 100 mL·min−1 for 3 h. After that, pure THFA with hydrogen was pumped into the reactor at a rate of 0.12 mL·h−1. Afterwards, the reactor was pressurized to 0.2~2.0 MPa with H2. The reaction temperature was in the range of 230–300 °C. The liquid products were analyzed by a gas chromatography (Agilent 6890N GC, Santa Clara, CA, USA) equipped with a flame ionization detector (FID) and an AB-FFAP capillary column (30 m × 0.32 mm × 0.25 μm). The THFA conversion and product selectivity were calculated based on the following equations:
conversion (%) = (moles of THFA charged-moles of THFA left)/moles of THFA charged × 100%
selectivity (%) = moles of a product generated/(moles of THFA charged-moles of THFA left) × 100%.

3.3. Characterization of Catalyst

XRD data was recorded on an XRD-7000 (Kyoto, Japan) using Cu Kα radiation (λ = 0.154 nm) produced by an X-ray source and operated at 40 kV and 30 mA. A scanning angle (2θ) ranged from 10 to 80°.
The BET surface areas of the catalysts were determined through N2 adsorption–desorption at −190 °C using a Quantachrome SI Instrument (Boynton Beach, FL, USA). Prior to measurements, all catalysts were degassed under vacuum at 100 °C for 10 min and at 300 °C for 3 h. Then, the specific surface area and BJH pore size distribution were calculated on the basis of the desorption branch of the isotherms.
The reducibility of the calcined catalysts was determined by H2-TPR, which was conducted on an Auto Chem. II2920 (Mircromeritics, Atlanta, FA, USA). Typically, 100 mg catalysts were outgassed in N2 at 300 °C for 1 h to remove impurities and then cooled down to room temperature. A mixture of 5 vol % H2 and 95 vol % He was passed through the catalyst bed (20 mL·min−1), while the temperature was increased from 40 to 800 °C at 15 °C·min−1.
The NH3-TPD analysis was also conducted on an Auto Chem. II 2920 (Mircromeritics, Atlanta, FA, USA). Approximately 100 mg catalysts were added to a quartz tube, pre-treated with He gas at 300 °C for 1 h, and then cooled down to room temperature. The catalysts were saturated with pure NH3 for 1 h. The samples were then cleaned with He gas at 50 °C to remove the physically adsorbed NH3. During the measurement, the temperature was raised to 800 °C at 10 °C·min−1 with the flow of He (50 mL·min−1) to desorb NH3. TEM were investigated using a JEM-2100F electron microscope (Akishima, Tokyo, Japan) at 200 kV.

4. Conclusions

The highly selective vapor-phase hydrogenolysis of THFA to THP was realized over a Cu–ZnO/Al2O3 catalyst prepared via precipitation–extrusion. The yield of THP is closely related to the ratio of Cu/Zn/Al, reaction temperature, and H2 pressure. At 270 °C and 1.0 MPa H2, the THP selectivity from THFA was up to 89.4% over the optimum Cu–ZnO/Al2O3 catalyst (the molar ratio of Cu/Zn/Al being 4:1:10). During the conversion of THFA to THP, it was found that three consecutive reactions were involved: (1) the rearrangement of THFA into 2-HTHP, (2) the dehydration of 2-HTHP to DHP, and (3) the hydrogenation of DHP to THP. The synergy of metal sites and medium acid sites is the key for a high catalytic activity for the production of THP from THFA.

Supplementary Materials

The supplementary materials are available online at https://www.mdpi.com/2073-4344/8/3/105/s1, Table S1: the comparison of results THF and THP as solvent, Figure S1: Particle volume-size distribution of the Cu-ZnO/Al2O3 catalysts, Figure S2: N2 physisorption isotherm of the Cu-ZnO/Al2O3 catalysts, Figure S3: NH3-TPD patterns of Cu-ZnO/Al2O3 catalysts with different γ-Al2O3.

Acknowledgments

This project was supported by the Beijing Natural Science Foundation (2184101).

Author Contributions

F.Z., B.Z. and L.H. conceived and designed the experiments; F.Z. performed the experiments; F.Z., X.W., L.H. and D.J., analyzed the data; S.D. and S.L. contributed materials and analysis tools; F.Z., B.Z., X.W., L.H. and L.M. wrote the paper.

Conflicts of Interest

The authors declare no conflict of interest.

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Catalysts 08 00105 g001 550
Figure 1. XRD patterns of calcined catalysts samples with different amount of γ-Al2O3.
Figure 1. XRD patterns of calcined catalysts samples with different amount of γ-Al2O3.
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Figure 2. H2-TPR profiles of the calcined catalyst samples.
Figure 2. H2-TPR profiles of the calcined catalyst samples.
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Figure 3. TEM image of the catalyst after reduction by H2.
Figure 3. TEM image of the catalyst after reduction by H2.
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Figure 4. Catalytic stability test of Cu–ZnO/Al2O3 (4:1:10 = Cu/Zn/Al). (Reaction conditions: temperature, 270 °C, 1.0 MPa H2, THFA: 99.9 wt %).
Figure 4. Catalytic stability test of Cu–ZnO/Al2O3 (4:1:10 = Cu/Zn/Al). (Reaction conditions: temperature, 270 °C, 1.0 MPa H2, THFA: 99.9 wt %).
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Scheme 1. Reaction pathway in the hydrogenolysis/hydrogenation of tetrahydrofurfuryl alcohol over the Cu–ZnO/Al2O3 catalyst in the gas phase.
Scheme 1. Reaction pathway in the hydrogenolysis/hydrogenation of tetrahydrofurfuryl alcohol over the Cu–ZnO/Al2O3 catalyst in the gas phase.
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Table
Table 1. The physicochemical properties of the catalysts.
Table 1. The physicochemical properties of the catalysts.
CatalystsCu/Zn/Al Molar RatioSBET (m2·g−1)Pore Volume (cc⋅g−1)Copper Crystalline Size (nm)Average Pore Size (nm)
A4-1-004:1:0041.30.1834.48.8
A0-0-010:0:10310.30.94-6.1
A4-1-034:1:03196.40.5426.64.7
A4-1-054:1:05199.30.6125.84.5
A4-1-074:1:07203.50.6325.03.9
A4-1-104:1:10223.80.6824.33.8
A4-1-154:1:15261.70.7022.33.6
Table
Table 2. Acidity distribution and chemical composition of the catalysts.
Table 2. Acidity distribution and chemical composition of the catalysts.
SamplesTemperature of NH3 Desportion Peaks (°C)Acid Account for Percentage Acid Amount (μmol·g−1)
T1T2T3Weak (%)Medium (%)Strong (%)Total
A0-0-0110827532450.036.113.97.2
A4-1-0010322533363.631.84.52.2
A4-1-0310322433266.730.42.910.2
A4-1-0510222733551.945.74.98.1
A4-1-0710622533647.148.24.78.5
A4-1-1010522633446.548.84.78.6
A4-1-1510322533046.747.85.49.2
Table
Table 3. Tetrahyrofurfuryl alcohol (THFA) conversion over different catalysts.
Table 3. Tetrahyrofurfuryl alcohol (THFA) conversion over different catalysts.
CatalystsConversion (%)Selectivity (%)
THP1-PentanolDVLDHP
A4-1-0011.531.32.12.134.5
A0-0-0123.11.50.118.074.4
A4-1-0338.951.84.216.413.0
A4-1-0568.148.712.814.312.4
A4-1-0766.669.310.112.62.5
A4-1-1078.677.88.68.11.6
A4-1-1557.463.63.521.14.6
Reaction condition: 255 °C, 0.6 MPa, THFA: 99.9 wt %.
Table
Table 4. Conversion of THFA over mechanical mixing and extrusion methods.
Table 4. Conversion of THFA over mechanical mixing and extrusion methods.
CatalystsConversion (%)Selectivity (%)
THP1-PentanolDVLDHP
A a57.768.84.618.23.2
B a36.477.90.670.3
A b9889.570.60
B b90.474.9122.60.8
a Reaction condition: 240 °C, 0.6 MPa; b Reaction condition, 280 °C, 0.6 MPa; A: extrusion; B: mechanical mixing.
Table
Table 5. Effect of reaction temperature on the conversion of THFA over A4-1-10.
Table 5. Effect of reaction temperature on the conversion of THFA over A4-1-10.
T(°C)Conversion (%)Selectivity (%)
THP1-PentanolDVLDHP
23037.755.22.5293.8
24057.768.84.618.23.2
25078.677.88.68.11.6
26091.986.87.330.8
27095.291.45.61.30.4
2809889.570.60
29099.385.97.50.20.1
Reaction pressure: 0.6 MPa, THFA: 99.9 wt %.
Table
Table 6. Effect of pressure on the conversion of THFA over A4-1-10.
Table 6. Effect of pressure on the conversion of THFA over A4-1-10.
P(MPa)Conversion (%)Selectivity (%)
THP1-PentanolDVLDHP
0.268.945.58.417.78.8
0.476.559.46.015.88.4
0.688.381.66.55.92.8
0.891.790.55.02.61.3
1.098.889.17.80.70.6
1.597.889.17.91.20.5
Reaction temperature, 250 °C, THFA: 99.9 wt %.

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MDPI and ACS Style

Zhang, F.; Zhang, B.; Wang, X.; Huang, L.; Ji, D.; Du, S.; Ma, L.; Lin, S. Synthesis of Tetrahydropyran from Tetrahydrofurfuryl Alcohol over Cu–Zno/Al2O3 under a Gaseous-Phase Condition. Catalysts 2018, 8, 105. https://doi.org/10.3390/catal8030105

AMA Style

Zhang F, Zhang B, Wang X, Huang L, Ji D, Du S, Ma L, Lin S. Synthesis of Tetrahydropyran from Tetrahydrofurfuryl Alcohol over Cu–Zno/Al2O3 under a Gaseous-Phase Condition. Catalysts. 2018; 8(3):105. https://doi.org/10.3390/catal8030105

Chicago/Turabian Style

Zhang, Fengyuan, Bin Zhang, Xincheng Wang, Long Huang, Dekun Ji, Songsong Du, Lei Ma, and Shijing Lin. 2018. "Synthesis of Tetrahydropyran from Tetrahydrofurfuryl Alcohol over Cu–Zno/Al2O3 under a Gaseous-Phase Condition" Catalysts 8, no. 3: 105. https://doi.org/10.3390/catal8030105

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