1070-4272/04/7701-0041C2004 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 77, No. 1, 2004, pp. 41! 45. Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 1,
2004, pp. 43! 47.
Original Russian Text Copyright + 2004 by Knyazev, Vodyankina, Kurina, Koshcheev, Boronin.
Cleaning of the Surface of Silver Crystals Used as Catalysts
of Gas-Phase Oxidation of Ethylene Glycol to Glyoxal
A. S. Knyazev, O. V. Vodyankina, L. N. Kurina, S. V. Koshcheev, and A. I. Boronin
Institute of Petroleum Chemistry, Siberian Division, Russian Academy of Science, Tomsk, Russia
Tomsk State University, Tomsk, Russia
Institute of Catalysis, Siberian Division, Russian Academy of Science, Novosibirsk, Russia
Received June 16, 2003
Abstract-The procedure for cleaning polycrystalline fibers of electrolytic silver used as a catalyst for gas-
phase oxidation of ethylene glycol to glyoxal was developed with the aid of X-ray photoelectron spectroscopy.
Unsupported compact metals are used as catalysts
of some important industrial reactions. The typical
feature of the catalytic reactions performed under rigid
conditions is segregation of impurities on the catalyst
surface. These impurities can partially or completely
poison the catalyst. As a result, the behavior of the
catalytic system at varied external parameters (tem-
perature and pressure of reactants) becomes irre-
producible. As a rule, the catalyst is contaminated by
the impurities contained in the initial material used for
the catalyst production or by impurities introduced in
the course of the catalyst production. The problem
of the surface cleanness arises for both pilot and in-
dustrial catalysts. Measurements of physicochemical
properties of contaminated compounds can be incor-
rect. Purification of these samples under rigorous con-
ditions (calcination, etching, etc.) can also make their
Silver is one of widely used metallic catalysts for
preparing ethylene oxide , formaldehyde, acetalde-
hyde, and glyoxal  by heterogeneous oxidation.
Practically important vapor-phase oxidation of ethyl-
ene glycol into glyoxal is catalyzed by both compact
and supported silver .
The best catalyst for glyoxal synthesis is polycrys-
talline silver fiber prepared by electrolysis of a silver
chloride melt . This catalyst has a unique nano- and
microstructure stable to reactive chemical media at
8003900 K. The results of the study of these silver
catalysts prepared by the electrolytic procedure make
a great contribution to the theory of heterogeneous
catalysis with metals. Fibrous silver catalysts should
be free of process and other impurities. However,
investigation of their surfcae by surface-sensitive
methods shows the presence of various impurities.
In this work, the states of surface atoms and the
chemical composition of the surface of silver fiber
samples taken in different steps of their preparation,
purification, and application as catalysts were studied
by X-ray photoelectron spectroscopy (XPS). Based on
the experimental data, a nondestructive procedure for
cleaning the surface of silver crystals with preserva-
tion of their morphological and structural features was
proposed. As determined by XPS, the surface of the
silver catalyst treated under actual catalytic conditions
is almost free of impurities.
Filamentary silver crystals were prepared by elec-
trolysis of an AgNO
melt in an open electrolysis bath
with a rotating cathode (T = 5433560 K, 32334 wt %
in a KNO
melt) . A scanning
electron microscopic (SEM) study shows that these
samples consist of silver needles with a smooth sur-
face (Fig. 1), which are formed by topochemical proc-
esses occurring in the course of electrolysis of the
melt of metal nitrates. Silver crystals formed under
these conditions have a developed dendrite structure
with a great number of surface defects .
The chemical composition of the surface of silver
catalyst was studied by XPS using a VG ESCALAB
spectrometer. The spectra were recorded by the proce-
dure described in detail in .
Electrons were emitted from the samples under the
action of soft AlK
X-ray radiation. The free path
of the electrons l was in the range 20330 A depend-
ing on their energy, which allowed the study of the
sample surface to a depth of 3l, i.e., 60390 A.
The samples were fixed in air in a holder with a