Article Cite This: Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
pubs.acs.org/IECR
Nb-Doped Vanadium Phosphorus Oxide Catalyst for the Aldol Condensation of Acetic Acid with Formaldehyde to Acrylic Acid Yumeng Wang, Zhenlu Wang, Xue Hao, Wenxiang Zhang, and Wanchun Zhu* Key Laboratory of Surface and Interface Chemistry of Jilin Province, College of Chemistry, Jilin University, Jiefang Road 2519, Changchun 130021, People’s Republic of China
Downloaded via DURHAM UNIV on August 29, 2018 at 22:23:24 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
S Supporting Information *
ABSTRACT: Nb-doped vanadium phosphorus oxide catalysts were prepared and characterized using a variety of methods, including XRD, FT-IR, XPS, TPD and BET. The catalysts were examined for their ability to promote the aldol condensation of acetic acid with formaldehyde to acrylic acid. Catalyst composition and the conditions used to prepare the catalysts were investigated for their effects on catalytic activity. The addition of Nb changes the properties and catalytic properties of the catalyst to some extent, especially the surface acidity of catalyst and the average valence of surface V atoms, which have the greatest influence on the catalyst. When Nb/V = 0.06, the catalyst surface has the greatest acidity, the valence of surface V atoms is the lowest, and the selectivity (83.4%) and yield of acrylic acid (18.1%) are maximized.
1. INTRODUCTION Acrylic acid is an important resin monomer used in the manufacture of various materials, including plastics, coatings, adhesives, elastomers and paints.1−10 The main method to produce acrylic acid is propene oxidation.4−6 Recently, the aldol condensation of acetic acid and formaldehyde to acrylic acid has shown promise as a potential new route and has attracted considerable interest due to several advantages, including the simplicity of the reaction process, low cost of raw materials, full use of resources, and environmentally benign reaction conditions. There are many patents and papers describing catalysts that convert acetic acid and formaldehyde into acrylic acid.11−20 The main catalyst system known to affect this transformation, a vanadium phosphorus oxide (VPO) catalyst, is also known for its ability to oxidize butane to maleic anhydride21−29 and for its use in some condensation reactions.16,30−34 Eastman Chemical Company has described a V, Ti, P mixed oxide catalyst19 and then modified the catalyst with alkali metal.20 BASF SE13 has invented a catalyst that includes VPO as an active ingredient, carrier and accelerator. Ai35 has studied the combination of vanadium pentoxide and phosphorus pentoxide. When P/V = 1.06−1.10, the prepared catalyst showed good catalytic activity when transforming acetic acid and formaldehyde into acrylic acid. However, a thorough understanding of the structural properties, reaction properties and reaction mechanism of VPO catalysts in the condensation reaction of acetic acid and formaldehyde is lacking and requires further research. To improve the catalyst performance, various modifications have been explored in the preparation of VPO catalysts. Taufiq-Yap et al.26 prepared VPO catalysts by using a hemihydrate precursor, VOHPO4·0.5H2O, for the oxidation © XXXX American Chemical Society
of n-butane to maleic anhydride. Various metal dopants (Zr, Zn, Ni, Nb, Mo, Mn, Fe, Cu, Cr, Ce and Co) were used to prepare doped nanosized VPO catalysts. These doped VPO catalysts proved beneficial due to changes in their redox properties, particle size and catalytic performances. Caldarelli et al.28 discussed the effect of Nb when used as a promoter for VPO catalysts in the oxidation of n-butane to maleic anhydride. Through the ex situ and operando/in situ experiments, it was shown that Nb plays two important roles. One, it promoted the oxidation of V+4 into V+5 under reaction conditions and, two, it promoted the surface transformation of other crystalline compounds into δ-VOPO4. In our present work, VPO catalysts doped with Nb were prepared and used in the reaction of acetic acid and formaldehyde to prepare acrylic acid. The effects of Nb content on the crystal phase, acidity, specific surface, average valence of surface V atoms and catalytic performance of the catalyst was investigated.
2. EXPERIMENTAL SECTION 2.1. Catalyst Preparation. Catalysts were prepared by the organic route as described below. 5 g of V2O5 was refluxed for 4 h at 110 °C in a mixture of benzyl and isobutyl alcohols. Niobium oxalate hydrate and orthophosphoric acid were added sequentially to the solution at 70 °C. After refluxing for 4 h at 110 °C, the obtained suspension was filtered and then dried at 100 °C overnight to yield the desirde catalyst Received: Revised: Accepted: Published: A
May 15, 2018 August 18, 2018 August 23, 2018 August 23, 2018 DOI: 10.1021/acs.iecr.8b02132 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research precursor. Finally, the catalyst precursor was calcined from room temperature to 400 °C at a rate of 3 °C/min. After a constant temperature of 2 h, the temperature was raised to 550 °C at a rate of 3 °C/min, and calcination was continued for 5 h to obtain the catalyst. The prepared catalyst was named as NbxVPO (x stands for the Nb/V molar ratio). 2.2. Catalyst Characterization. Powder X-ray diffraction (XRD) was carried out using a Shimadzu diffractometer (model XRD-6000) with Cu Kα radiation (30 kV and 40 mA) and a scan step of 10°·min−1 in the 2θ range of 10 to 70°. Fourier transform infrared spectroscopy (FT-IR) was obtained at room temperature using a Nicolet Impact 410 spectrometer. The solid samples were prepared using KBr as a diluent. X-ray photoelectron spectroscopy (XPS) was measured on a ESCA LAB 250 Type X-ray photoelectron spectrometer manufactured by Thermo. The 284.6 eV value of polluted carbon C 1s was used as the nuclear effect of the internal standard calibration sample. Total acidity of catalysts was measured by temperatureprogrammed desorption of NH3 (NH3-TPD). The catalysts (50 mg) were thermally treated at 550 °C with flowing N2 for 30 min and then cooled to 100 °C prior to adsorption. After purging the physically adsorbed NH3, the system was heated to 600 °C in flowing He. The amount of chemisorbed ammonia was detected with a TCD detector. The total surface area and pore size of the catalysts were measured in a Micromeritics ASAP 2010 instrument using BET and BJH methods from the adsorption isotherms of N2 adsorption at 77 K. The catalyst samples were degassed at 200 °C before measurement. 2.3. Catalytic Evaluation. The aldol condensation of acetic acid and formaldehyde (molar ratio HAc/HCHO = 3.5/ 1) to produce acrylic acid (AA) was carried out in a fixed-bed reactor packed with 1 mL of catalyst. The reactor was fabricated from an φ 5 mm × 150 mm stainless steel tube, which was mounted vertically at the heating furnace. The acetic acid solution was mixed with trioxymethylene and then fed from the top of the reactor by a micro injection pump with the feed rate of 1 mL·h−1. The product was passed through a six-way valve and then into a gas chromatograph for online analysis. The specific calculation process is as follows: The conversion of acetic acid n − nresidual HAc C HAc = initial HAc × 100% ninitial HAc
Figure 1. XRD patterns of VPO and NbxVPO precursors.
84-0761) phases. When Nb/V = 0.06, the diffraction peak intensity is the greatest, especially at 30.6°, which can be assigned to (130) planes. When Nb/V ≥ 0.06, a diffraction peak appeared at 27.5°. It may belong to the NbPO5 (JCPDS 19-0868) phases. Figure 2 shows the XRD patterns of VPO and NbxVPO catalysts. The diffraction lines at 2θ = 19.5°, 22.0°, 24.2°, 28.5°
Figure 2. XRD patterns of VPO and NbxVPO catalysts.
The selectivity of acrylic acid n produced AA SAA = × 100% ninitial HAc − nresidual HAc
and 34.7° were typical of the δ-VOPO4 (JCPDS 47-0951) phases and can be assigned to (002), (111), (012), (020) and (022) planes. Otherwise, the diffraction lines at 2θ = 12.3° were typical of the (VO)3P4O13 (JCPDS 50-0418) phases and can be assigned to (122) planes. When Nb/V = 0.06, the diffraction peak intensity at 12.3° is greater than any other catalysts. This shows that the proportion of V4+ in the catalyst plays an important role. No relevant crystalline phase of Nb was found in the catalysts. It is likely due to the low content and amorphous form of Nb. 3.1.2. FT-IR Analysis. Figure 3 shows the FT-IR spectra of VPO and NbxVPO precursors. The band at 3373 cm−1 belongs to the stretching vibration absorption peak of O−H. The peaks
The yield of acrylic acid YAA = C HAcSAA × 100%
3. RESULTS AND DISCUSSION 3.1. Catalyst Characterization. 3.1.1. XRD Analysis. The XRD patterns of VPO and NbxVPO precursors are shown in Figure 1. All of the precursors have diffraction peaks at 15.6°, 19.8°, 24.3°, 28.8°, 30.6°, 32.1°, 33.9°, 34.5°, 37.5°, 47.9° and 49.2°, which are attributed to the VOHPO4·0.5H2O (JCPDS B
DOI: 10.1021/acs.iecr.8b02132 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research
3.1.3. XPS Analysis. The chemical states of V on the surfaces of VPO and NbxVPO catalysts were investigated by Xray photoelectron spectroscopy (XPS) as shown in Figure 5.
Figure 3. FT-IR spectra of VPO and NbxVPO precursors.
appearing at 2358, 2329 and 1635 cm−1 are attributed to the bending vibration absorption peaks of the coordinated water molecules. The bands at 1197, 1103 and 1056 cm−1 are the asymmetric stretching vibration absorption peak of PO3. The peaks at 1130 and 640 cm−1 belong to the bending vibration absorption peaks of POH. The bands at 971, 925 and 539 cm−1 correspond to the stretching vibration absorption peak of VO, the stretching vibration absorption peak of P(OH) and the bending vibration absorption peaks of OPO, respectively. This is consistent with the infrared spectrum of the VOHPO4·0.5H2O crystal phase.36 Figure 4 shows the FT-IR spectra of VPO and NbxVPO catalysts. The bands at 1430 and 1024 cm−1 belong to the
Figure 5. V 2p3/2 curve fittings of VPO and NbxVPO catalysts.
The binding energies of V 2p3/2 of these catalysts were in the range of 518.66−518.87 eV. Through curve-fitting analysis, V4+ and V5+ species on the catalyst surface can be distinguished depending on their characteristic binding energy. The corresponding binding energies and average valence of V are summarized in Table 1. For VPO catalysts, the average valence of V is 4.84. For NbxVPO catalysts with increased Nb content, the average valence of V is reduced. When Nb/V = 0.06, the average valence of V is the lowest (4.77) and when the Nb content is increased further, the average valence of V begins to increase. 3.1.4. BET Surface Area Analysis. Table 2 shows the structure parameters of VPO and NbxVPO catalysts. For VPO catalysts, the specific surface area is 19.5 m2·g−1, the pore volume is 0.0882 cm3·g−1 and the average pore size is 15.8 nm. In general, the introduction of Nb reduces the specific surface area of the catalyst, reducing the pore volume and the average pore size. With increasing Nb content, the specific surface area of the catalyst progressively increases and when Nb/V = 0.06, the catalyst has the largest specific surface area (17.4 m2·g−1). With continued increase in Nb content, the specific surface area of the catalysts begins to decrease. 3.1.5. NH3-TPD Analysis. NH3-TPD was carried out to measure the surface acidity of the VPO and NbxVPO catalysts. As shown in Figure 6, the NH3 desorption peaks for all the catalysts appeared at the temperature range of 150−320 °C, which corresponds to the weak-middle acid sites. The desorption peak of NH3 in the temperature range of 320− 500 °C corresponds to strong acid sites. As shown in Figure 7, peak-fitting analysis indicated three NH3 desorption peaks, which correspond to weak, middle and strong acid sites, respectively. As summarized in Table 3, the acid quantities of the catalysts were calculated according to their NH3 desorption peak area. For the VPO catalyst, the total acid quantity is the highest (163.3 μmolNH3/g), but the strong acid proportion is the lowest, 36.61%. With the addition of Nb, the total acid quantity decreased, but the relative content of strong acid (relative to weak-middle acid quantity) increased compared with VPO catalyst. When Nb/V = 0.06, the quantity of strong
Figure 4. FT-IR spectra of VPO and NbxVPO catalysts.
stretching vibration absorption peaks of VO. The peaks appearing at 642 cm−1 are attributed to the bending vibration absorption peaks of POH. The peaks at 985 and 579 cm−1 belong to the PO, VO stretching vibration absorption peaks of VOPO4. C
DOI: 10.1021/acs.iecr.8b02132 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research Table 1. XPS Results for VPO and NbxVPO Catalysts Binding energy of V 2p3/2 (eV) Average valence of V
VPO
Nb0.02VPO
Nb0.04VPO
Nb0.06VPO
Nb0.08VPO
Nb0.10VPO
518.74 4.84
518.66 4.94
518.84 4.87
518.87 4.77
518.87 4.85
518.82 4.89
the conversion of acetic acid is 25.3%, the selectivity of acrylic acid is 68.6%, and the yield of acrylic acid is 17.3%. Overall, the introduction of Nb reduces the conversion of acetic acid and improves the selectivity of acrylic acid. With increased Nb content, the conversion of acetic acid showed little change, but the selectivity and yield of acrylic acid progressively increased. When Nb/V = 0.06, the selectivity (83.4%) and yield of acrylic acid (18.5%) are maximized and continued increase in Nb content gave reduced selectivity and yield. Taking into account the chemical states of V on the surface of the catalysts, it was concluded that the lower the average valence of V, the higher the selectivity and yield of acrylic acid. These results show that the addition of a certain amount of niobium helps to reduce the average valence of V. When Nb/V = 0.06, the average price of V is optimal and the selectivity and yield of acrylic acid is the highest. For the VPO catalyst, the total acid quantity is the highest (163.3 μmolNH3/g), but it is not conducive to improving the selectivity of acrylic acid. On the other hand, the strong acid proportion of the VPO catalyst is the lowest, 36.61%. It can be seen that strong acid sites are more important than weakmiddle acid sites. The introduction of Nb changes the relative strength of the acid center and improves the selectivity for acrylic acid. For the NbxVPO catalyst, when Nb/V = 0.06, the quantity (48.2 μmolNH3/g) of strong acid and the total acid quantity (118.0 μmolNH3/g) is more than any other NbxVPO catalyst. Thus, a larger total acid quantity and a certain amount of strong acid sites help to improve the conversion of acetic acid and the selectivity of acrylic acid. 3.2.2. Catalytic Performance of Nb0.06VPO Catalysts with Different P/V Molar Ratios. The influence of the P/V molar ratio on the conversion and selectivity of the Nb0.06VPO catalysts is presented in Table S1. With an increase in the P/V molar ratio, the conversion of acetic acid progressively decreases. When P/V = 1.4, the conversion of acetic acid is the lowest and continued increase in the P/V molar ratio increases the conversion of acetic acid. However, the selectivity and yield of acrylic acid has the opposite trend. With an increase in the P/V molar ratio, the selectivity and yield of acrylic acid progressively increases. When P/V = 1.4, the selectivity and yield of acrylic acid is the highest, and continued increase in the P/V molar ratio decreases the conversion of acetic acid. Adding a certain amount of P could increase the selectivity and yield of acrylic acid. However, when the P/V molar ratios exceed 1.4, accelerated degradation of acetic acid leaded to a decrease in the selectivity and yield of acrylic acid. In summary, the optimal P/V molar ratio is 1.4. 3.2.3. Catalytic Performance of Nb0.06VPO Catalysts with Different Reductive Agents. Table S2 shows the catalytic performance of Nb0.06VPO catalysts prepared with different reductive agents. The catalyst prepared with isobutanol and benzyl alcohol as the reducing agent gave lower conversion of acetic acid, but higher selectivity and yield of acrylic acid. The purpose of isobutanol is to dissolve V2O5 to form soluble V5+ alkoxide, whereas benzyl alcohol reduces the solubility of V5+
Table 2. Structure Parameters of VPO and NbxVPO Catalysts Catalyst
BET surface area (m2·g−1)
Pore vol. (cm3·g−1)
Pore size (nm)
VPO Nb0.02VPO Nb0.04VPO Nb0.06VPO Nb0.08VPO Nb0.10VPO
19.5 5.80 12.5 17.4 16.0 10.7
0.0882 0.0178 0.0657 0.0439 0.0535 0.0439
15.8 12.1 17.1 6.40 13.2 10.5
Figure 6. NH3-TPD profiles of VPO and NbxVPO catalysts.
Figure 7. Peak fitting results of NH3-TPD profiles of VPO and NbxVPO catalysts.
acid (48.2 μmolNH3/g) and the total acid quantity (118.0 μmolNH3/g) is more than any other NbxVPO catalyst. 3.2. Effects of Catalyst Composition and Preparation Conditions on Catalytic Performance. 3.2.1. Catalytic Performance of VPO and NbxVPO Catalysts with Different Nb/V Molar Ratios. The catalytic performance of VPO and NbxVPO catalysts is presented in Table 4. For VPO catalysts, D
DOI: 10.1021/acs.iecr.8b02132 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research Table 3. NH3-TPD Results of VPO and NbxVPO Catalysts Catalyst VPO
Nb0.02VPO
Nb0.04VPO
Nb0.06VPO
Nb0.08VPO
Nb0.10VPO
Peak center (°C)
Peak area
Acid quantity (μmolNH3/g)
Total acid quantity (μmolNH3/g)
Acid quantity proportion (%)
187.8 251.2 389.4 172.0 216.8 393.2 189.9 246.1 388.7 189.2 260.4 403.4 186.8 252.3 404.1 182.6 239.6 397.0
619.2 1024.1 949.1 66.4 235.7 452.9 340.3 667.5 616.1 365.2 715.8 747.5 293.9 363.6 514.4 280.4 428.8 537.3
39.0 64.5 59.8 4.3 15.1 29.0 21.6 42.4 39.1 23.6 46.2 48.2 19.0 23.5 33.3 18.0 27.5 34.5
163.3
23.89 39.50 36.61 8.80 31.23 60.01 20.96 41.11 37.94 19.97 39.13 40.87 25.08 31.03 43.90 22.49 34.41 43.12
48.4
103.1
118.0
75.9
79.9
the best, the catalytic activity is the highest, the specific surface area is the largest, the average valence of V is the lowest and the surface acidity is optimal. The acidity on the catalyst surface and the average valence of surface V atoms play an important role in catalytic performance. The lower the average valence of V is, the higher the selectivity and yield of acrylic acid are. The addition of a certain amount of niobium helps to reduce the average valence of V. A larger total acid quantity and a certain amount of strong acid sites are beneficial for the protonation of formaldehyde, which promotes the formation of acrylic acid and reduces the occurrence of side reactions to obtain high selectivity.
Table 4. Catalytic Performance of VPO and NbxVPO Catalysts with Different Nb/V Molar Ratiosa Catalyst
Conv. of HAc (%)
Selec. of AA (%)
Yield. of AA (%)
VPO Nb0.02VPO Nb0.04VPO Nb0.06VPO Nb0.08VPO Nb0.10VPO
25.3 17.6 23.5 22.2 22.2 20.1
68.6 57.2 69.3 83.4 71.8 56.4
17.3 10.0 16.3 18.5 16.0 11.3
a
The reaction condition: amount of catalysts 1 mL; HAc/HCHO = 3.5/1; volume of feedstock 1 mL·h−1; flow of N2 20 mL·min−1; flow of O2 3 mL·min−1; reaction temperature 350 °C (HAc, acetic acid; AA, acrylic acid).
■
ASSOCIATED CONTENT
* Supporting Information S
37
alkoxide. Therefore, the optimal reductive agent is a mixture of isobutanol and benzyl alcohol. 3.2.4. Catalytic Performance of Nb0.06VPO Catalysts Prepared with Different Temperatures. Table S3 shows the catalytic performance of Nb0.06VPO catalysts prepared using different temperatures. With catalyst prepared under increased temperatures, the conversion of acetic acid showed little change, but the selectivity and yield of acrylic acid progressively increased. When the synthesis temperature is 110 °C, the selectivity and yield of acrylic acid are maximized, and continued increase in the synthesis temperature gave decreased selectivity and yield of acrylic acid. Thus, the optimal synthesis temperature is 110 °C.
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.8b02132. Catalytic performance of Nb0.06VPO catalysts with different P/V molar ratios; catalytic performance of Nb0.06VPO catalysts prepared by different reductive agents; catalytic performance of Nb0.06VPO catalysts prepared with different temperatures (PDF)
■
AUTHOR INFORMATION
Corresponding Author
*W. Zhu. E-mail:
[email protected]; Fax: +86 0431 85168420; Tel: +86 0431 88964193. ORCID
4. CONCLUSIONS The optimal conditions for the preparation of a NbxVPO catalyst were obtained through optimization of the experimental conditions. The suitable reductive agent is a mixture of isobutanol and benzyl alcohol. The best synthesis temperature is 110 °C. The optimal V/P/Nb atomic ratio is 1/1.4/0.06. The NbxVPO catalyst precursor belongs to the VOHPO4· 0.5H2O crystal phase, and after calcination, it is converted into a mixed phase of δ-VOPO4 and (VO)3P4O13. With different Nb contents, the specific surface area, surface acidity and catalytic performance of the catalyst are affected to varying degrees. When Nb/V = 0.06, the selectivity of the catalyst is
Wanchun Zhu: 0000-0001-6337-0517 Notes
The authors declare no competing financial interest.
■ ■
ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (21473074). REFERENCES
(1) Neher, H. T.; Kelton, S. C., Jr. Preparation of Acrylic Esters. U.S. Patent 2582911, January 15, 1952.
E
DOI: 10.1021/acs.iecr.8b02132 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research (2) Reppe, W.; Stadler, R. Process Producing Acrylate Acid. U.S. Patent 3023237, February 27, 1962. (3) Pan, T.; Scates, M. O.; Shaver, R. D.; Torrence, G. P.; Chapman, J. T.; Mueller, S. Process for Making Acrylic Acid by Integrating Acetic Acid Feed Stream from Carbonylation Process. U.S. Patent 2014/0073812(A1), March 13, 2014. (4) Mizuno, N.; Tateishi, M.; Iwamoto, M. Pronounced catalytic activity of Fe0.08Cs2.5H1.26PVMo11O40 for direct oxidation of propane into acrylic acid. Appl. Catal., A 1995, 128, L165−L170. (5) Ueda, W.; Suzuki, Y. Partial Oxidation of Propane to Acrylic Acid over Reduced Heteropolymolybdate Catalysts. Chem. Lett. 1995, 24, 541−542. (6) Ai, M. Oxidation of propane to acrylic acid on V2O5-P2O5-based catalysts. J. Catal. 1986, 101, 389−395. (7) Wilhelm, R.; Ulrike, W.; Andreas, T. Process for the Catalytic Gas-Phase Oxidation of Acrolein to Acrylic Acid. DE Patent 4431949(A1), January, 1995. (8) Devaux, J. F.; Fauconner, M. Method for Producing BioResourced Polymer-Grade Acrylic Acid from Glycerol. FR Patent 2935971(Al), November 11, 2010. (9) Herzog, S.; Altwasser, S.; Mueller-Engel, K. J. Process for Preparing Acrylic Acid from Methanol and Acetic Acid. U.S. Patent 2012/0071688(Al), March 22, 2012. (10) Herzog, S.; Altwasser, S.; Ottenbacher, M.; Huetten, F.; Wentink, A. E.; Schaefer, A. Process for Preparing Acrylic Acid from Ethanol and Formaldehyde. U.S. Patent 2013/0289305(A1), October 31, 2013. (11) Nagaki, D.; Peterson, C.; Scates, M.; Weiner, H.; Chapman, J. T.; Locke, A. S. Catalysts for Producing Acrylic Acids and Acrylates. U.S. Patent 2013/0085293(A1), April 4, 2013. (12) Parvulescu, A. N.; Lange De Oliveira, A.; Lejkowski, M.; Woerz, N. T.; Hartmann, M.; Amakawa, K.; Goebel, M.; Mueller, U.; Feyen, M.; Liu, Y. Process for Preparing Acrylic Acid Using an AluminumFree Zeolitic. U.S. Patent 2015/0343431(A1), December 3, 2015. (13) Liu, Y.; Dleterle, M.; Woerz, M. T.; Parvulescu, A. N.; Lejkowski, M.; Lieberknecht, J.; Walsdorff, C.; Amakawa, K. Process for Preparing Acrylic Acid. U.S. Patent 2016/0152541(A1), June 2, 2016. (14) Brueggemann, T. C.; Woerz, N. T.; Ruppel, A. Process for Preparing Acrylic Acid from Formaldehyde and Acetic Acid. U.S. Patent 2016/0176797(A1), June 23, 2016. (15) Woerz, N. T.; Schulz, L.; Blaschke, T.; Hartmann, M.; Ruether, F.; Li, Y. Process for Obtaining Acrylic Acid. U.S. Patent 2016/ 0159724(A1), June 9, 2016. (16) Nagaki, D.; Weiner, H.; Chapman, J. T.; Scates, M. O.; Locke, A. S.; Peterson, C. J. Catalysts for Producing Acrylic Acids and Acrylates. U.S. Patent 2012/0289743(A1), November 15, 2012. (17) Goebel, M.; Waladorff, C.; Hartmann, M.; Woerz, N. T.; Blaschke, T.; Gruene, P. Process for Preparing Acrylic Acid with High Space-Time Yield. U.S. Patent 2014/0343319(A1), November 20, 2014. (18) Nagaki, D.; Pan, T.; Peterson, C. J.; Bowden, E.; Chapman, J. T.; Mueller, S. Catalyst for Producing Acrylic Acids and Acrylates. U.S. Patent 2013/0245312(A1), September 19, 2013. (19) Norman, D. W.; Tustin, G. C.; Nash, M. J.; Deng, L.; Barnette, T. S. Process for Preparing V-Ti-P Catalysts for Synthesis of 2,3Unsaturated Carboxylic Acids. U.S. Patent 2013/0072715(A1), March 21, 2013. (20) Norman, D. W.; King, G. A. Process for Preparing Modified VTi-P Catalysts for Synthesis of 2,3-Unsaturated Carboxylic Acids. U.S. Patent 2013/0072716(A1), March 21, 2013. (21) Irusta, S.; Boix, A.; Pierini, B.; Caspani, C.; Petunchi, J. Effect of Mo on the active sites of VPO catalysts upon the selective oxidation of n-butane. J. Catal. 1999, 187, 298−310. (22) Pierini, B. T.; Lombardo, E. A. Cr, Mo and W used as VPO promoters in the partial oxidation of n-butane to maleic anhydride. Catal. Today 2005, 107, 323−329.
(23) Taufiq-Yap, Y. H.; Yuen, C. S.; Suziana, N. M. N.; Irmawati, R. Effects of Bi and Ni on the properties of a vanadium phosphorus oxide catalyst. Chin. J. Catal. 2014, 35, 270−276. (24) Guliants, V. V.; Benziger, J. B.; Sundaresan, S.; Wachs, I. E.; Hirt, A. M. Effect of promoters for n-butane oxidation to maleic anhydride over vanadium-phosphorus-oxide catalysts: comparison with supported vanadia catalysts. Catal. Lett. 1999, 62, 87−91. (25) Pries de Oliveira, P. G.; Eon, J. G.; Chavant, M.; Riche, A. S.; Martin, V.; Caldarelli, S.; Volta, J. C. Modification of vanadium phosphorus oxides used for n -butane oxidation to maleic anhydride by interaction with niobium phosphate. Catal. Today 2000, 57, 177− 186. (26) Taufiq-Yap, Y. H.; Suziana, N. M. N.; Hussein, M. Z. Influences of the various metal dopants for the nanosized vanadium phosphate catalysts. Catal. Lett. 2011, 141, 136−148. (27) Taufiq-Yap, Y. H.; Rownaghi, A. A.; Hussein, M. Z.; Irmawati, R. Preparation of vanadium phosphate catalysts from VOPO4•2H2O: effect of microwave irradiation on morphology and catalytic property. Catal. Lett. 2007, 119, 64−71. (28) Caldarelli, A.; Banares, M. A.; Cortelli, C.; Luciani, S.; Cavani, F. An investigation on surface reactivity of Nb-doped vanadyl pyrophosphate catalysts by reactivity experiments and in situ Raman spectroscopy. Catal. Sci. Technol. 2014, 4, 419−427. (29) Duarte de Farias, A. M.; Gonzalez, W. D. A.; Pries de Oliveira, P. G.; Eon, J. G.; Herrmann, J. M.; Aouine, M.; Loridant, S.; Volta, J. C. Vanadium phosphorus oxide catalyst modified by niobium doping for mild oxidation of n-butane to maleic anhydride. J. Catal. 2002, 208, 238−246. (30) Ai, M. Effect of the composition of vanadium-titanium binary phosphate on catalytic performance in vapor-phase aldol condensation. Appl. Catal. 1989, 54, 29−36. (31) Ai, M. Preparation of high-surface-area titanium-vanadium binary pyrophosphate catalysts. Appl. Catal. 1989, 48, 51−61. (32) Yang, D.; Li, D.; Yao, H. Y.; Zhang, G. L.; Jiao, Y. Y.; Li, Z. X.; Li, C. S.; Zhang, S. J. Reaction of formalin with acetic acid over vanadium−phosphorus oxide bifunctional catalyst. Ind. Eng. Chem. Res. 2015, 54, 6865−6873. (33) Hu, J.; Lu, Z. P.; Yin, H. B.; Xue, W. P.; Wang, A. L.; Shen, L. Q.; Liu, S. X. Aldol condensation of acetic acid with formaldehyde to acrylic acid over SiO2-, SBA-15-, and HZSM-5-supported V-P-O catalysts. J. Ind. Eng. Chem. 2016, 40, 145−151. (34) Yang, D.; Sararuk, C.; Suzuki, K.; Li, Z. X.; Li, C. S. Effect of calcination temperature on the catalytic activity of VPO for aldol condensation of acetic acid and formalin. Chem. Eng. J. 2016, 300, 160−168. (35) Ai, M. Vapor-phase aldol condensation of formaldehyde with acetic acid on V2O5-P2O5 catalysts. J. Catal. 1987, 107, 201−208. (36) Busca, G.; Cavani, F.; Centi, G.; Trifiro, F. Nature and mechanism of formation of vanadyl pyrophosphate: Active phase in n -butane selective oxidation. J. Catal. 1986, 99, 400−414. (37) Cornaglia, L. M.; Sanchez, C. A.; Lombardo, E. A. Chemistry of vanadium-phosphorus oxide catalyst preparation. Appl. Catal., A 1993, 95, 117−130.
F
DOI: 10.1021/acs.iecr.8b02132 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
