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Influence of doped ZrO2 on the selective oxidation of methanol to methylformate on vanadium oxide catalysts.
H.E.Curry-Hyde and R.F. Howe (Editors), Naiural Gas Conversion I1 0 1994 Elsevier Science B.V. All rights reserved.
383
Influence of doped ZrO, on the selective oxidation of methanol to methylformate on vanadium oxide catalysts. R. Ukropec, J.G. van Ommen, P.D.L. Mercera, K.Seshan and J.R.H. Ross Faculty of Chemical Technology, University of Twente, P.O.Box 217,7500 AE Enschede, The Netherlands. 1. Introduction. It is well known that methanol can be oxidized to formaldehyde in the presence of air and Ag or V205-based catalysts. Next to the formaldehyde production a small amount of methylformate, is produced. Methylformate is a versatile and attractive intermediate for a number of chemicals (such as, formic acid, acetic acid, formamide, dimethyl carbonate, methylglycolate and ethyleneglycol). Methylformate at the moment is manufactured by carbonylation of methanol in liquid phase in the presence of basic catalysts, at high CO pressures (1). Alternative routes in the gasphase are i) dehydrogenation of methanol on Cu-based catalysts (2) or ii) the oxidation of methanol over different metal oxide catalysts, like V205-based catalysts which are suitable for production of methylformate (3). Zirconia is chemically more inert to methanol than the classical supports. It has a high surface area, which can be stabilised with dopes such as Y,O, and La2OY It was found that activity and selectivity of monolayer V205 catalysts for oxidation of methanol to methylformate is dependent on dopes in the support. In the presented work we have studied V205 100. monolayer or submonolayer catalysts on ZrO, and ZrO, doped with Y,O, and La209
2. Experimental. The supports were prepared by hydrolyzing mixtures of zirconium- and yttrium- or lanthanum-alkoxides with water, followed by drying at llO°C for 15 hours and calcining at 45OOC for 15 hours. The catalysts were prepared by adsorbing VO(acac), from a toluene solution at 110°C for 15 hours, followed by calcining at 450°C for two hours. loo 140 la0 220 260 3#) The oxidation of methanol has been studied Tenpetetue (C) in a fixed bed reactor at temperatures 0 = x,,,~,,; + = !+qg; 0 = s~fq;A = s;, between 100°C and 3OO0C, 200mg of catalyst = s,; = ;,,,,s t 200mg SO,, flow feed was 50 ml/min Figure 1 ZrYS-V1 consisting of 4.3 vol % methanol, 24 vol % 0, and 71.7 vol % He. ~
384
3. Results. In figure 1 a typical example of the conversion of methanol and the selectivity to the products changing with temperature is given. This yttrium doped catalyst gives a high selectivity to methyl formate (maximum 75% at 200°C). Formaldehyde is the most important byproduct, a very small amount of dimethoxymethane is detected, CO and CO, are formed in larger quantities at temperatures higher than 200°C. The surface areas of lanthanum and yttrium doped catalysts are comparable. In table 1 the results of the catalyst preparation are given different amounts of vanadium oxide prepared via adsorption on yttrium and lanthanum doped and undoped zirconias. The code of the catalysts for example: ZrY5-Vl is zirkoonoxide with 5 mole% of Y01.5 and about 1wt% of V and ZrLa2-2V1 this is zirkoonoxide with 2 mole% La203 and two times the adsorption of the same amount vanadium resulting normally in about twice the amount of V1( = 1 wt% V), which is about 2 wt% vanadium. Table 1
Characterization of Supports and Catalysts
Catalyst
Support (mol %) Y0i.s La01.s
ZrYs-Vl ZrYs-V2 ZrYs-V3 ZrYs-V4 ZrYs-2V1
4.82 4.83 4.94 4.82 5.17
Zrh-Vl ZrLa2-2V1 ZrLal-2V1 Zrb5-V1 Zr02-V1 Zr0,-V2 Zr02-V3 Zr02-V4 Zr02-2V2
S-BET (m2/g)
Catalyst V loading wt. % at.V/nm2
-----------
68.3 67.2 59.2 59.7 84.3
1.32 2.34 3.44 4.52 2.25
2.28 4.12 4.87 8.95 2.94
---
-------
3.39 4.00 2.43 1.41
29.1 69.5 71.5 71.4
0.84 1.90 2.00 1.90
3.41 3.23 3.31 3.15
---
---
-_-__
---
___
36.2 35.1 34.7 33.9 72.9
0.34 0.61 0.76 1.33 1.11
1.10 1.90 2.40 4.20 1.80
---
---
---
---
In table 2 the conversion and selectivities are given for a number of catalysts consisting of V,Os supported on Y- or La-oxide doped Zr02 Increasing the amount of V,O, increases the activity of both the Y-and La-containing catalysts, but only in the case of yttrium the selectivity to methylformate decreases (and to formaldehyde increases). With increasing the amount of La, a decreasing activity of the catalysts is found, while the selectivity to methylformate is not changed. Doping zirconia with yttrium appears to result in higher selectivities to methylformate. One lanthanum doped catalysts (ZrLa2V1) has a much lower surface area, which has apparently only an effect on the activity (conversion of 11%). In table 3 the results for the undoped V,O,/ZrO, catalysts are presented. Unfortunately the surface areas of these catalysts are much smaller than is
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measured for the doped catalysts except for the catalyst Zr02-2V2. For this catalyst about the same activity and selectivity is found as for the yttrium doped one (ZRY5-Vl). The same trend is found as for the yttrium doped catalysts, with increasing V,O, content activity increases, while selectivity to methylformate decreases (and selectivity to formaldehyde increases). Table 2
Methanol-oxydation over V20s on Zr02-X0,.S supports. X = Y or La
Catalyst
Conv Selectivities (mol %) Catalyst mol% MF FH DMOM
ZrY,--Vl ZrY,--V2 ZrY,--V3 ZrY5--V4 ZrY5-2V1
57.8 84.8 93.7 92.3 73.1
74.7 63.9 46.0 40.6 80.1
17.5 24.2 31.3 43.7 14.4
ZrLa2--V1 Zr%-2V1 ZrLal-2V1 Zr&,-Vl
11.7 35.0 57.5 63.3
55.6 61.2 59.4 59.5
25.6 27.9 33.3 35.0
---
-----
---
-----
3.00 1.20 1.10
Table 3
ZrO,--Vl Zr02--V2 Zr0,--V3 Zr0,--V4 Zr02-2V2
Methanol-oxidation over V2Os on ZrO, supports Conv Selectivities (mol %) mol% MF FH DMOM 27.8 61.0 70.0 80.0 59.0
73.8 62.3 60.0 47.5 72.7
19.6 31.3 33.8 46.3 20.4
2.50 0.80
---
-----
MF = Methylfotmate FH = formaldehyde DMOM = Dimethoxymethane
4. Discussion The activity increases with increasing V205 content on doped as well as on undoped supports, which detrimental to selectivity to methylformate. Doping with lanthanum decreases the activity and selectivity dramatically. The more lanthanum is present the less active the catalyst is. Possibly Lanthanum forms an inactive compound with V20s. ESCA measurements indicate mixed oxide formation between this dope and vanadium. Yttrium has a beneficial effect on the selectivity to methylformate, it can give higher conversion and at the same time higher selectivities than vanadium on zirconia, although this can also be due to the higher surface area of these catalysts. However in both cases (doped and undoped zirconias) a low coverage by V205 seem to be beneficial for the metylformate formation. Possibly the uncovered support plays an important role in the methylformate formation, possibly by increasing the formation of the necessary methoxy groups.
References 1. BASF, Brit. Pat. 252,848 (22.4.1925), Chem. Abstr.,21,2477 (1925) 2. M. Yoneoka, M. Osugi ( Mitsubishi Gas Chemicals ): U.S.Pat. 2,753,634 (8.6. 1978), Chem. Abstr., 89, 75263j (1978) 3. A.J. van Hengstum, J.G. van Ommen, H. Bosch and P.J.Gellings, in Proc. 8th Int. Congr. Catal., Berlin( 1984), Verlag Chemie Weinheim (1984), Vol. 4,p. 297
383
Influence of doped ZrO, on the selective oxidation of methanol to methylformate on vanadium oxide catalysts. R. Ukropec, J.G. van Ommen, P.D.L. Mercera, K.Seshan and J.R.H. Ross Faculty of Chemical Technology, University of Twente, P.O.Box 217,7500 AE Enschede, The Netherlands. 1. Introduction. It is well known that methanol can be oxidized to formaldehyde in the presence of air and Ag or V205-based catalysts. Next to the formaldehyde production a small amount of methylformate, is produced. Methylformate is a versatile and attractive intermediate for a number of chemicals (such as, formic acid, acetic acid, formamide, dimethyl carbonate, methylglycolate and ethyleneglycol). Methylformate at the moment is manufactured by carbonylation of methanol in liquid phase in the presence of basic catalysts, at high CO pressures (1). Alternative routes in the gasphase are i) dehydrogenation of methanol on Cu-based catalysts (2) or ii) the oxidation of methanol over different metal oxide catalysts, like V205-based catalysts which are suitable for production of methylformate (3). Zirconia is chemically more inert to methanol than the classical supports. It has a high surface area, which can be stabilised with dopes such as Y,O, and La2OY It was found that activity and selectivity of monolayer V205 catalysts for oxidation of methanol to methylformate is dependent on dopes in the support. In the presented work we have studied V205 100. monolayer or submonolayer catalysts on ZrO, and ZrO, doped with Y,O, and La209
2. Experimental. The supports were prepared by hydrolyzing mixtures of zirconium- and yttrium- or lanthanum-alkoxides with water, followed by drying at llO°C for 15 hours and calcining at 45OOC for 15 hours. The catalysts were prepared by adsorbing VO(acac), from a toluene solution at 110°C for 15 hours, followed by calcining at 450°C for two hours. loo 140 la0 220 260 3#) The oxidation of methanol has been studied Tenpetetue (C) in a fixed bed reactor at temperatures 0 = x,,,~,,; + = !+qg; 0 = s~fq;A = s;, between 100°C and 3OO0C, 200mg of catalyst = s,; = ;,,,,s t 200mg SO,, flow feed was 50 ml/min Figure 1 ZrYS-V1 consisting of 4.3 vol % methanol, 24 vol % 0, and 71.7 vol % He. ~
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3. Results. In figure 1 a typical example of the conversion of methanol and the selectivity to the products changing with temperature is given. This yttrium doped catalyst gives a high selectivity to methyl formate (maximum 75% at 200°C). Formaldehyde is the most important byproduct, a very small amount of dimethoxymethane is detected, CO and CO, are formed in larger quantities at temperatures higher than 200°C. The surface areas of lanthanum and yttrium doped catalysts are comparable. In table 1 the results of the catalyst preparation are given different amounts of vanadium oxide prepared via adsorption on yttrium and lanthanum doped and undoped zirconias. The code of the catalysts for example: ZrY5-Vl is zirkoonoxide with 5 mole% of Y01.5 and about 1wt% of V and ZrLa2-2V1 this is zirkoonoxide with 2 mole% La203 and two times the adsorption of the same amount vanadium resulting normally in about twice the amount of V1( = 1 wt% V), which is about 2 wt% vanadium. Table 1
Characterization of Supports and Catalysts
Catalyst
Support (mol %) Y0i.s La01.s
ZrYs-Vl ZrYs-V2 ZrYs-V3 ZrYs-V4 ZrYs-2V1
4.82 4.83 4.94 4.82 5.17
Zrh-Vl ZrLa2-2V1 ZrLal-2V1 Zrb5-V1 Zr02-V1 Zr0,-V2 Zr02-V3 Zr02-V4 Zr02-2V2
S-BET (m2/g)
Catalyst V loading wt. % at.V/nm2
-----------
68.3 67.2 59.2 59.7 84.3
1.32 2.34 3.44 4.52 2.25
2.28 4.12 4.87 8.95 2.94
---
-------
3.39 4.00 2.43 1.41
29.1 69.5 71.5 71.4
0.84 1.90 2.00 1.90
3.41 3.23 3.31 3.15
---
---
-_-__
---
___
36.2 35.1 34.7 33.9 72.9
0.34 0.61 0.76 1.33 1.11
1.10 1.90 2.40 4.20 1.80
---
---
---
---
In table 2 the conversion and selectivities are given for a number of catalysts consisting of V,Os supported on Y- or La-oxide doped Zr02 Increasing the amount of V,O, increases the activity of both the Y-and La-containing catalysts, but only in the case of yttrium the selectivity to methylformate decreases (and to formaldehyde increases). With increasing the amount of La, a decreasing activity of the catalysts is found, while the selectivity to methylformate is not changed. Doping zirconia with yttrium appears to result in higher selectivities to methylformate. One lanthanum doped catalysts (ZrLa2V1) has a much lower surface area, which has apparently only an effect on the activity (conversion of 11%). In table 3 the results for the undoped V,O,/ZrO, catalysts are presented. Unfortunately the surface areas of these catalysts are much smaller than is
385
measured for the doped catalysts except for the catalyst Zr02-2V2. For this catalyst about the same activity and selectivity is found as for the yttrium doped one (ZRY5-Vl). The same trend is found as for the yttrium doped catalysts, with increasing V,O, content activity increases, while selectivity to methylformate decreases (and selectivity to formaldehyde increases). Table 2
Methanol-oxydation over V20s on Zr02-X0,.S supports. X = Y or La
Catalyst
Conv Selectivities (mol %) Catalyst mol% MF FH DMOM
ZrY,--Vl ZrY,--V2 ZrY,--V3 ZrY5--V4 ZrY5-2V1
57.8 84.8 93.7 92.3 73.1
74.7 63.9 46.0 40.6 80.1
17.5 24.2 31.3 43.7 14.4
ZrLa2--V1 Zr%-2V1 ZrLal-2V1 Zr&,-Vl
11.7 35.0 57.5 63.3
55.6 61.2 59.4 59.5
25.6 27.9 33.3 35.0
---
-----
---
-----
3.00 1.20 1.10
Table 3
ZrO,--Vl Zr02--V2 Zr0,--V3 Zr0,--V4 Zr02-2V2
Methanol-oxidation over V2Os on ZrO, supports Conv Selectivities (mol %) mol% MF FH DMOM 27.8 61.0 70.0 80.0 59.0
73.8 62.3 60.0 47.5 72.7
19.6 31.3 33.8 46.3 20.4
2.50 0.80
---
-----
MF = Methylfotmate FH = formaldehyde DMOM = Dimethoxymethane
4. Discussion The activity increases with increasing V205 content on doped as well as on undoped supports, which detrimental to selectivity to methylformate. Doping with lanthanum decreases the activity and selectivity dramatically. The more lanthanum is present the less active the catalyst is. Possibly Lanthanum forms an inactive compound with V20s. ESCA measurements indicate mixed oxide formation between this dope and vanadium. Yttrium has a beneficial effect on the selectivity to methylformate, it can give higher conversion and at the same time higher selectivities than vanadium on zirconia, although this can also be due to the higher surface area of these catalysts. However in both cases (doped and undoped zirconias) a low coverage by V205 seem to be beneficial for the metylformate formation. Possibly the uncovered support plays an important role in the methylformate formation, possibly by increasing the formation of the necessary methoxy groups.
References 1. BASF, Brit. Pat. 252,848 (22.4.1925), Chem. Abstr.,21,2477 (1925) 2. M. Yoneoka, M. Osugi ( Mitsubishi Gas Chemicals ): U.S.Pat. 2,753,634 (8.6. 1978), Chem. Abstr., 89, 75263j (1978) 3. A.J. van Hengstum, J.G. van Ommen, H. Bosch and P.J.Gellings, in Proc. 8th Int. Congr. Catal., Berlin( 1984), Verlag Chemie Weinheim (1984), Vol. 4,p. 297