Formation of peroxo radicals on tin dioxide

Formation of peroxo radicals on tin dioxide

Hooff, van, J. H. C., & van Helden, J. F. (1967). Formation of peroxo radicals on tin dioxide. Journal of Catalysis, 8(2), 199-200. https://doi.org/10.1016/0021-9517(67)90304-1

DOI:

10.1016/0021-9517(67)90304-1

Document status and date: Published: 01/01/1967

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XOTES

Formation

of Peroxo Radicals on Tin Dioxide

As previously reported, it is possible to

show the formation of peroxo radicals on

slightly reduced titanium dioxide and zinc oxide with the ESR method (1). From new

experiments it is concluded that similar

phenomena occur on tindioxide. When

- + 20 OC ----. -,hO oc : ,** _. II 1: ‘-b250e jr q”artz

FIG. 1. (a) ESR spectrum as observed on SnOl after contacted with 02; 02 pressure, 3 torr. (b) Separate ESR signals.

oxygen is added to tin dioxide, pretreated during 4 hr at 500°C and under a vacuum of 10T3 torr, the ESR spectrum shown in Fig. 1 can be observed. This spectrum is very similar to that obtained with titanium dioxide except for a difference in its tem-

perature dependency. Whereas the TiO,

signals are strongly dependent on tempera-

2-a T=-150°C

2-b

2-c

FIG. 2. IESR spectra as observed on SnOz after contacted with a mixture of oxygen and 1-butene: a, immediately after addition; b, after 3 hr; c, after 100 hr.

200 NOTES

ture, the spectrum obtained from SnO, is

almost the same at room temperature and

at -160°C.

In spite of this difference we would like to interpret these spectra on similar lines. Three different signals occur simultane-

ously in the ESR spectrum: Signal c, a

broad almost symmetric signal with g =

2.010; Signal d, a narrow three g value signal with g, = 2.033, g2 = 2.005, g3 =

the perpendicular and linear arrangement

can only occur with metal ions with empty or partly filled cl orbitals. Accordingly Zn*+

with the electron configuration [Ar] 3d’O

does not show these bonding structures.

However, as Sn4+ with the electron con- figuration [Kr] 4d1° did show the signals ascribed to these arrangements, we have to conclude, to outer shell bonding (5d orbit- als) in this case.

. .

M-2,

. .

.p. . . d

Angular Perpendicular Linear

1.986; Signal e, a narrow three g value signal with g1 = 2.029, g2 = 2.010, g3 = 2.004.

When a mixture of 1-butene and oxy-

gen is added, the three oxygen signals can be observed again. However, Signal e

decreases slowly and finally disappears,

while Signal d remains nearly unaltered (Fig. 2). This is an additional proof for the correctness of the interpretation of the spectrum.

Each of the signals, c, d, and e, is sup- posed to correspond with a special form of adsorbed molecular oxygen. Signal c corre- sponds with the linear, Signal d with the perpendicular, and Signal e with the angu- lar arrangement. As explained in ref. (1)

It is further interesting that butene addi-

tion removed the signal assigned to a

species that is similar to a radical in the classical sense, i.e., with a single electron in an atomic orbital.

1.

REFERENCE

CORNAZ, P. F., VAN HOOFF, J. H. C., PLUIJM,

F. J., AND SCTIUIT, G. C. A., Discussions

Faraduy sot. 41, 290 (1966).

J. H. C. VAN HOOFF

J. F. VAN HELDEN Dept. of Inorganic Chemistry

Technological University Eindhoven The Netherlands

Received March 2S, 1967

A Relationship between Infrared Frequencies of Adsorbed

Carbon Monoxide and Metal Electron Population

As part of a wider investigation a study interdependent is suggested by expressing has been made of the perturbation of vibra- observed frequencies as the valence-electron

tional frequency of the carbon monoxide content E(C0) of the adsorbed carbon

molecule following adsorption as “linear monoxide species using the formula of

carbonyl” on face-centered cubic transition Gardner and Petrucci (1). E(C0) is clearly metals. A rather uniform increase in fre- integral for gaseous forms of carbon mon- quency with increase in electronic specific oxide but may be nonintegral for adsorbed

heat constant ye1 of the bulk metal was _{species. Figure 1 shows that a reasonably}