QUANTUM-CHEMICAL INVESTIGATION OF ALCOHOLS DEHYDRATION AND DEHYDROGENATION POSSIBILITY IN INTERFACE LAYERS OF VANADIUM OXIDE SYSTEMS Текст научной статьи по специальности «Химические науки»

QUANTUM-CHEMICAL INVESTIGATION OF ALCOHOLS DEHYDRATION AND DEHYDROGENATION POSSIBILITY IN INTERFACE LAYERS OF VANADIUM OXIDE SYSTEMS

N.V. KHOKHRIAKOV, V.l. KODOLOV, O.A. NIKOLAEVA, V.L. VOLKOV*

Basic research-educational center of chemical physics and mesoscopy Udmurt Scientific center, Ural Division, RAS, 7 Studencheskaya St., Izhevsk, 426069 e-mail: kodol@istu.udm.ru

♦Institute of Solids Chemistry, Ural Division, RAS, Ekaterinburg

ABSTRACT. Quantum-chemical investigation of the interaction of vanadium oxide lamellar structures and polyvanadic acid fragments with ethanol, which has been chosen as the interaction model of polyvinyl alcohol with polyvanadic acid, is carried out. It is shown that dehydration and dehydrogenation processes are caused by transitions of -OH groups to vanadium atom, and hydrogen atoms - to oxygen atoms of vanadium oxide pyramids, which form plane layers. In accordance with calculations and experimental data, the stabilization of lamellar vanadium oxide structures is reached with the layer charge -2. The formation possibility of polyene structures and carbon tubules from polyvinyl alcohol in polyvanadic acid and its derivatives, containing transition metals, is experimentally confirmed.

INTRODUCTION

In recent years the data regarding the low temperature synthesis methods of substances, polymer products as well, in interface layers of vanadium oxide systems (V) have appeared [1-3]. In this connection the studying of the processes, connected with the mobility of hydrogen atoms and hydrogen-containing groups during the interaction of chemical panicles in complex processes, by quantum-chemical methods, is of interest.

The purpose of this investigation is to determine the alcohols dehydration possibility with the following dehydrogenation and polymerization during their interaction with the layers of vanadium oxide systems, on the example of vanadium oxide and vanadic acids and ethanol.

1. DESCRIPTION OF POSSIBLE STRUCTURES BEING FORMED DURING THE INTERACTION AND METHODS OF THEIR CALCULATION

Vanadium oxide or its acids mixed with ethyl alcohol are chosen as system models. Vanadium oxide layers are formed from pyramids in the center of each of them a vanadium atom is located, and oxygen atoms - on tops. The neighboring pyramids are connected via oxygen bridges. In vanadium oxide the pyramids have an irregular shape: four oxygen atoms

XWVIHHECKAfl OH3HKA M ME30CK0riMfl. Tom 3, № 1

of each pyramid are connected with vanadium atom of neighboring pyramids, and the fifth oxygen atom is orientated out of the limits of the layer and its free valences are partly compensated by the interactions with vanadium atom of one of the pyramids of the neighboring layer (Fig. 1).

As the task consisted in the studying of the reactions in interface layers of vanadic acids, free valances of oxygen atoms are compensated by the interactions with hydrogen atoms. Further, the interaction of ethanol molecule with the only vanadium oxide layer is considered. When the molecules of ethyl alcohol are introduced into the medium, the partial transition of hydrogen atoms from carbons of alcohol molecule to oxygen of vanadium oxide with the following separation of this hydrogen under the electric field action is possible. The formation of charged or neutral molecular fragments shown in Fig. 2-5 is possible.

To imitate the endless layer of V2O5 pyramids the fragments consisting of one (Fig. 6) or two pyramids connected via an oxygen bridge (Fig. 7, 8, 9) are used.

Two types of fragments containing two pyramids are considered and their energy optimization is carried out. In the fragment shown in Fig. 7 the stopped bonds of all oxygen atoms are compensated by hydrogen atoms. Thus, the stopped bond compensation with vanadium atoms of neighboring layers, water molecules, as well as the possible transition of hydrogen atom from ethyl alcohol to vanadium oxide layer are taken into consideration. In the fragments shown in Fig. 8, 9 the stopped bonds of oxygen atoms, orientated out of the layer, remain. The fragment shown in Fig. 4 was electric-neutral and decomposed as a result of energy optimization.

54

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H(7)

H(6l

I

0(3;

C{2)

H(4) H(5)

Fig. 2. Scheme of fragment containing ethanol molecule in which Hydrogen Atoms were broken away from C (2) and C (1)

H(8

Initial structure

H(6)H(7) C(2J

.0(3)

H(4 r H(5)

Fig. 3. Fragment containing of the ethanol molecule (without one Hydrogen Atom). The charge equals -1

H(8)

Optimized structure

H(6\H(7) C(2)

I

0(3)

CO^ H(4) H(5)

Fig. 4. The structure of Fig.3 after energy optimization

H(8)

.0(3)

C(2J

H(4) H(5) H(6)

Fig. 5. Scheme of ethanol molecule in which Hydrogen atom was broken away from C (2). The charge equals -1

.H(9)

0(4)

H(ll) / H(10) I I

\ 0(6) I

0(5) —V(2)

■0(3)

\

H(8)

0(1)

H(7)

Fig. 6. Optimized structure V (OH)

Hp 01

w.

H(19)tO|l 5)

\

0(5}

7<> °H|uP H|18)

0[5J

-VI2] HP)

.m

■0(3)

Fig. 7. Optimized structure with two tetrahedrons V209H8 (Charge 0)

56

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H<9) ol6>

H,,\ H(!,\

OM 4) 0(5) 0(4) ~

X

^ 0(3) -H(7)

Vil I) , H(IS)

1 ' 0(l 2)

I

I

0(1)

0(10)

0(13) \

H(16)

Fig. 8. Optimized structure with two tetrahedrons V^OgHô (Charge 0)

0|1D| OH!

\ /

vn HfaO'l2)

^'o(12H|15] 0[41

°0 31 HI8J?P\

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Fig. 9. Optimized structure with two tetrahedrons V209H6 (Charge -2)

Quantum-chemical calculations are fulfilled by ab-initio using program product

GAMESS.

1. EXPERIMENTAL

Polyvinyl alcohol is mixed with the solution of polyvanadic acid containing molybdenum ions in the ratio 1:2-rl:3. The mixture is placed between carbon electrodes and electrostatic voltage 12 V is produced. The reaction mass color changing to black is observed in anode zone. Then the mass is heated at 90 °C during 2-3 hours, and all the mass acquires stable black color. The products obtained are washed by water and organic solvents. The resulted black powder is investigated by transmission electron microscopy, microdiffraction and X-ray photoelectron spectroscopy.

XMMMMECKAfl OM3HKA M ME30CK0nMR Tom 3, Ns 1

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3. RESULTS AND DISCUSSION

After quantum-chemical calculations it is found out that pyramids stabilization is possible if the layers are negatively charged, thus corresponding to experimental data [5]. It is necessary to mention that the calculated geometrical structure of the pyramids is a bit different from the experimental. The calculation results of energies, charge and geometrical parameters of the products are given in Tables 1-3.

The negatively charged complex is stable. It is also necessary to note that the geometrical structure of the pyramids obtained during the calculations is a bit different from the experimental [1].

Table 1. Compound energies (Hartree)

Energies of ethanol fragments

In geometry of After optimization C2H5OH

C2H5OH -154,0647 -154,0647

C2H3OH -152,7802 -152,8773

C2H40H(-l)a -153,3622 -153,3819

C2H40H(-l)b -153,3626 -153,3773

C2H30H(-2) -152,4568 -152,7127 Energies of vanadium oxide systems V(OH)s -1320,1247 V2O9H8 -2564,2503 V209H6 -2563,0164 V209H6(-2) -2563,1272

Table 2. Geometric parameters of clusters on the base on Vanadium Oxide (V)

V(OH)5 V(12)-0(13) 1,76 V(2)-0(3) 1,91

Bond lengths V(12)-0(14) 1,81 V(2)-0(4) 1,88

0(l)-V(2) 1,78 V(12)-0(15) 1,75 V(2)-0(5) 1,79

0(l)-H(7) 0,95 0(15)-H(19) 0,95 V(2)-0(6) 1,87

V(2)-0(3) 1,78 Bond angles 0(5)-V(11) 1,79

V(2)-0(4) 1,80 0(l)-V(2)-0(3) 98,52 0(10)-V(11) 1,58

V(2)-0(5) 1,78 0(l)-V(2)-0(4) 115,27 V(11)-0(12) 1,87

58

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V(2)-0(6) 1,73 0(1 )-V(2)-0(5) 88.26 V(11)-0(13) 1,91

0(4)-H(9) 0,95 0(l)-V(2)-0(6) 118.56 V(ll)-0(14) 1,88

Bond angl es 0(3)-V(2)-0(4) 92.83 Bond angles

0(l)-V(2)-0(3) 87.62 0(3)-V(2)-0(5) 173,11 0(l)-V(2)-0(3) 104,35

0(l)-V(2)-0(4) 161,47 0(3)-V(2)-0(6) 90,32 0(l)-V(2)-0(4) 108,50

0(l)-V(2)-0(5) 86,96 0(4)-V(2)-0(5) 85.29 0(l)-V(2)-0(5) 106,49

0(l)-V(2)-0(6) 100,56 0(4)-V(2)-0(6) 124.89 0(l)-V(2)-0(6) 108,49

0(3)-V(2)-0(4) 85,24 0(5)-V(2)-0(6) 85,36 0(3)-V(2)-0(4) 81,91

0(3)-V(2)-0(5) 134,81 V(2)-0(3)-H(8) 146,22 0(3)-V(2)-0(5) 149,17

0(3)-V(2)-0(6) 112,68 V(2)-0(4)-H(9) 122,60 0(3)-V(2)-0(6) 82,13

0(4)-V(2)-0(5) 86,00 V(2)-0(5)-V(12) 147,35 0(4)-V(2)-0(5) 88,53

0(4)-V(2)-0(6) 97,96 0(5)-V(12)-0(l 1) 86,86 0(4)-V(2)-0(6) 142,27

0(5)-V(2)-0(6) 112,42 0(5)-V(12)-0(13) 89,91 0(5)-V(2)-0(6) 87,99

V(2)-0(4)-H(9) 125,38 0(5)-V(12)-0(14) 171,27 V(2)-0(5)-V(l 1) 152,21

V209H8 0(5)-V(12)-0(15) 96,62 0(5)-V(l l)-O(lO) 106,52

Bond lengths 0(11)-V(12)-0(13) 120,74 0(5)-V(l 1 )-0( 12) 87,98

0(1)-V(2) 1,71 0(11)-V(12)-0(14) 87,51 0(5)-V(l 1)-0(13) 149,11

V(2)-0(3) 1,74 0(11)-V(12)-0(15) 119,91 0(5)-V(l 1)-0(14) 88,58

V(2)-0(4) 1,79 0(13)-V(12)-0(14) 87,24 0(10)-V(11)-0(12) 108,47

V(2)-0(5) 1,85 0(13)-V(12)-0(15) 119,24 0(10)-V(11)-0(13) 104,36

V(2)-0(6) 1,77 0(14)-V(12)-0(15) 91,97 0(10)-V(11)-0(14) 108,47

0(5)-V(12) 1,73 V2OsH6(-2) 0(12)-V(11)-0(13) 82,12

0(6)-H(10) 0,95 Bond lengths 0(12)-V(11)-0(14) 142,32

0(11)-V(12) 1,82 0(1)-V(2) 1,58 0(13)-V(11)-0(14) 81,86

Table 3. Parameters of chemical bonds in clusters on the base on Vanadium Oxide (V)

bond | length 1 order atom Charge (by Mulliken) Charge (by Löwdin) Free valence

V(OH)5

0(1)-V(2) 1,775 0,877 0(1) -0,833 -0,416 1,744

0(1)-H(7) 0,949 0,790 V(2) 1,968 0,259 4,549

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59

V(2)-0(3) 1,783 0,878 0(3) -0,803 -0,401 1,747

V(2)-0(4) 1,801 0,851 0(4) -0,842 -0,450 1,703

V(2)-0(5) 1,780 0,889 0(5) -0,791 -0,393 1,761

V(2)-0(6) 1,726 0,959 0(6) -0,763 -0,344 1,805

0(3)-H(8) 0,952 0,795 H(7) 0,412 0,350 0,816

0(4)-H(9) 0,950 0,795 H(8) 0,409 0,344 0,818

0(5)-H(10) 0,951 0,795 H(9) 0,408 0,342 0,820

0(6)-H(ll) 0,949 0,773 ЩЮ) 0,410 0,347 0,817

H(ll) 0,426 0,362 0,799

V209Hg

0(l)-V(2) 1,711 1,124 0(1) -0,682 -0,292 1,921

0(1)-H(7) 0,975 0,738 V(2) 2,003 0,315 4,493

V(2)-0(3) 1,739 0,910 0(3) -0,861 -0,393 1,744

V(2)-0(4) 1,792 0,777 0(4) -0,858 -0,417 1,634

V(2)-0(5) 1,850 0,661 0(5) -0,894 -0,281 1,823

V(2)-0(6) 1,767 0,906 0(6) -0,754 -0,376 1,795

0(3)-H(8) 0,945 0,772 H(7) 0,465 0,382 0,762

0(4)-H(9) 0,951 0,796 H(8) 0,434 0,360 0,795

0(5)-V(12) 1,726 1,048 H(9) 0,411 0,348 0,815

0(6)-H(10) 0,953 0,788 H(10) 0,415 0,353 0,810

0(11)-V(12) 1,821 0,699 0(11) -0,898 -0,449 1,571

0(11)-H(16) 0,950 0,802 V(12) 1,943 0,249 4,596

V(12)-0(13) 1,763 0,982 0(13) -0,747 -0,361 1,809

V(12)-0(14) 1,814 0,810 0(14) -0,873 -0,480 1,642

V(12)-0(I5) 1,746 0,945 0(15) -0,767 -0,352 1,800

0(13)-H(17) 0,961 0,782 H(16) 0,414 0,345 0,815

0(14)-H(18) 0,948 0,801 H(17) 0,437 0,355 0,788

0(15)-H(19) 0,951 0,787 H(18) 0,401 0,340 0,825

H(19) 0,413 0,355 0,812

I J I V2O9H6

0(1)-V(2) 1,545 2,192 0(1) -0,391 -0,046 2,305

V(2)-0(3) 1,734 0,879 V(2) 1,703 0,219 4,791

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ХИМИЧЕСКАЯ ФИЗИКА И МЕЗОСКОПИЯ. Том 3, № 1

V(2)-0(4) 1,791 0,679 0(3) -0.861 i -0,398 | 1,714

V(2)-0(6) 1,727 0,962 0(4) -0,949 -0,469 1,503 I

0(3)-H(7) 0,944 0,769 0(5) -0,466 -0.102 2,246

0(4)-H(8) 0.948 0,783 0(6) -0,809 j -0.371 1,777

0(5)-V(ll) 1,557 2,110 H(7) 0,435 0,359 0,789

0(6)-H(9) 0.952 0,749 H(8) 0,423 0,355 0.804

0(10)-V(11) 1,806 0,835 H(9) 0,442 0,366 0,794

0(10)-0(13) 1,442 0,746 O(10) -0,389 -0,152 1,630

V(11)-0(12) 1,716 0,965 V(ll) 1.642 0,196 4,913

V(ll)-0(13) 2,576 0,080 0(12) -0,803 -0,372 1,786

V(11)-0(14) 1,729 0,854 0(13) -0,406 -0,225 i 1,651

0(12)-H(15) 0,960 0,743 0(14) -0,864 -0,404 1,699

0(13)-H(16) 0,956 0,822 H(15) 0,468 0,372 0,748

0(14)-H(17) 0,943 0,768 H(16) 0,388 0.315 0,829

H(17) 0,435 0,358 0,789

While modeling, the changes of interaction energy of hydrogen atom with cluster V(OH)5, proton transition from one water molecule to the other are studied (Fig. 10-12).

-2563,45 -2563,5 -2563,55 i -2563,6 1 -2563,65 -2563,7 -2563,75

Fig. 10. The energy change of Hydrogen transfer between centers in Vanadium Oxide

Fig. 11. The energy change of Hydrogen attraction to fragment V04(")

Fig. 12. The energy change of hydrogen transfer to other molecule of water

The direct modeling of chemical interaction of ethyl alcohol molecule with complexes containing two V2O5 pyramids is also carried out. The case when all oxygen atoms are bound with hydrogen atoms in the complex is considered (Fig. 13), as well as the case when each

Fig. 13. Scheme of ethanol interaction with Vanadium Oxide fragment in which Oxygen atoms are connected with Hydrogen

62

XUMVNECKA* OH3HKA M pE^OpKOnM*. Tom 3, № 1

Fig. 14. Scheme of ethanol interaction with Vanadium Oxide fragment having two non compensated Oxygen atoms and the charge -2

During the model experiment shown in Fig. 14 two hydrogen atoms from ethyl alcohol molecule transfer to oxygen atom of one of vanadium pyramids and to oxygen bridge atom. This proves the possibility of ethyl alcohol dehydrogenation in the interaction process with flat layer of vanadium oxide.

Further, the interaction of the products formed can lead to formation of tubules. This is confirmed by experimental results. For example, tubules have been obtained from polyvinyl alcohol in polyvanadic acid with the charged layer -1 containing molybdenum. In Fig. 15 there is a structure and microdiffraction of such tubule with the diameter 154 nm.

Fig. 15a. Microphotograph of nanotube obtained from PVA into polyvanadic acid containing Molybdenum

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63

Ось трубки

1010*

• • •

1

®

0002

• •• •

Fig. 15 b, c. Microdiffractogram of nanotube and its interpretation

In Fig. 15a it is seen that the tube is lamellar, the distance between the layers being 11,04 nm, this is approximately 30 times higher than the distance between the planes - 0,344 nm, characteristic for graphite. It is known that if there are defects in nanotubes or one of the

layers is partly absent, there is the possibility for lamellar nanotubes that the distance between the layers will increase [9]. In our case the distance between the layers is larger by an order than it is given in literature. We explain this phenomenon by a very great transverse dimension of the tubes investigated. The formation of such elongated structures with diameters up to several hundreds nanometers can be explained by the fact that polyvinyl alcohol macromoleculcs form lamellar aggregates. The reconstruction of interface formations, proceeding with surface energy decrease, leads to the formation of rather elongated tubular structures.

Clear reflexes with tension bars directed perpendicular to the tube axis are observed in microdiffraction patterns (Fig. 15b). Reflexes 1010 are split into two and are located by both sides of the tube axis, and this is characteristic for tubules [10]. The decoding scheme is shown in Fig. 15c. The common chirality angle of the tube is 15-16°. The given microdiffraction coincides rather well with the calculated diffraction for one-layer ideal nanotube given in paper [11].

REFERENCES

1. H.J. Muhr, F. Krumeich et al. Advanced Materials, 2000, v.12, N 3, p.231-236

2. F. Krumeich, H.J. Muhr et al. J.Am.Chem.Soc, 1999, v.121, N 36, p.8324-8333

3. V.I. Kodolov, O.A. Nikolaeva, L.G. Makarova et al. Chem. Physics and Mesoscopy, 2000, v.2, N 2, p. 164-170 (in Russian)

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ХИМИЧЕСКАЯ ФИЗИКА И МЕЗОСКОПИЯ. Том 3, № 1

4. A.A. Fotiev, A.A. Ivakin. Vanadium compounds of alkali metals and their formation conditions. Sverdlovsk: AS of USSR, Ural Branch, 1970, 153p (in Russian)

5. V.R. Volkov, G.S. Zakharova, V.M. Bondarenko. Xerogels of simple and complex poly vanadates. Ekaterinburg: RAS, UD, 2001, 194 p (in Russian)

6. N.V. Khokhriakov, V.l. Kodolov, O.Yu. Boldenkov, Prepr. In 2nd Int. Internet conference on Synthesis, investigation and application of metal - containing tubules. May - July, 2001; www.ugr.es/local/gmdm/intemet/

7. T.H. Dimming J.Chem. Phys. 1971, v.55, p. 716-723

8. M.W. Schmidt et al. J.Comp. Chem., 1993,v.l4,p. 1347-1363

9. D. Bernaents, A. Zettl, G. Chopra Nasreen et al. Electron diffraction study of single-wall carbon nanotubes. - Solid State Com., 1998, 105, №3, p. 145 - 149.

10. Yu. E. Lozovik, A.M. Popov. Formation and growth of carbon nanostructures - fullerens, nanoparticles, nanotubes and cones. UFN(Rus). 1997, v. 167, p. 751 - 774.

11. Bemaerts D., Op de Beeck M., Amelinckx S. tn st. The chirality of carbon nanotubules determined by dark-field electron microscopy. - Phil. Mag. A., 1996, 74, №3, p. 723 -740.

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