- Email: [email protected]
Auger spectroscopy study on copper-nickel alloy surfaces related to the catalysis
SURFACE SCIENCE 26 (1971) 313-316 0 North-Holland Publishing Co.
AUGER
SPECTROSCOPY SURFACES
STUDY
RELATED
ON COPPER-NICKEL
ALLOY
TO THE CATALYSIS
Received 29 December 1970 Studies on the copper-nickel alloys have been of special interest in seeking the fundamental bases of catalysis by alloys associated with the electronic structure. We have studied the catalytic properties of copper-nickel alloys after various surface treatments, by using fairly clean surface of the alloys in sheets by means of the ultra-high vacuum apparatus. The catalytic activity of alloys was found to increase more than several tens of times by the argon ion bombardmentl) or the oxidation-reduction treatmentz). Table 1 shows several examples for catalytic activity of pure nickel and 60 wt:! Cu-Ni alloy. It is to be noted that the catalytic activity of the alloy was increased by each treatment several more tens of times than that before treatment, the activity of the alloy being much greater than that of pure nickel after the same treatment. It could be concluded that the large increases in the catalytic activity of the alloy might result from the production of lattice defects or active centers at the surface due to the ion bombardment or the oxidation-reduction treatment. In order to clarify the nature of the active sites produced by such treatments, it must be useful to determine the average Cu-Ni ratio in the surface layer which might be changed by the treatments. In the present letter, applying Auger electron spectroscopy, changes in the average Cu-Ni ratio in the surface layers of the alloy which showed rather high catalytic activity with the surface treatments have been observed. A display type LEED apparatus with four spherical grids was used as an energy analyzer for Auger electrons. The details of argon ion bombardment technique have been described elsewheres). Here, we have particularly paid attention on the Auger spectra around 100 eV in energy, since the nearly surface layers should be surely important in relation to catalytic properties. The peak structure in the higher energy region of 700 to 1000 eV was observed to be similar to the results reported by Harris4). However, lower energy spectra were more sensitive to the surface treatments. Fig. 1 represents the differentiated spectra from pure Ni, pure Cu and 60 wt% Cu-Ni alloy, showing considerable change in surface composition with the treatments. Derivative peaks for pure Ni and Cu appeared at 101 313
-_-
Oxidation-reduction PO, = 2.3 Torr 5OO”C, 1 min PHz = 16 3OO”C, 2 Torr hr
500 ev 80 A/cm2 5 min
Argon ion bombardment
Surface treatment
TABLET
Before treatment After treatment
Before treatment After treatment
Hydrogen = deuterium = exchangeg) P”uz P”D2 1.5 Torr 1OOOC
.--.-
Before treatment After treatment
.
__
Ethylene hydrogenation2) POcziip = P”Hz = I.5 Torr 100°C
Ethylene hydrogenation’) P”C,H, = PH, = 1.5Torr 40°C
Catalytic reaction
-I-
.--_.._-
_
1.0 0.18
3.2
1.o
-__.
I.0 2.1
Nickel
Relative catalytic activity
Catalytic properties of Ni and 60 wt “/oCu-Ni alloy with surface treatments
_
._
0.04 20.7
0.12 19.2
0.31 27.4
---
Cu-Ni alloy
AUGERSPECTROSCOPYSTUDYON
and 105 eV, respectively,
as shown
in
Cu-Ni
315
ALLOY
fig. 1. The electron
energies
of these
peaks were found not to be changed by any treatment. In the spectra from the alloy surfaces, on the other hand, various peak shapes were obtained for the treatments, as seen in spectrum 1 to 4. In the case of non-treatment, spectrum 1, a couple of positive peaks at 99 and 102.5 eV, corresponding to Ni and Cu positive peaks, respectively, were observed. After the ion bombardment, as in spectra 2 and 3, the positive peak at 99 eV (Ni) became to be relatively strong and the other at 102.5 eV (Cu) to disappear. In con-
90
100 Electron
110 Energy
(eV)
Fig. 1. Auger spectra, dN(E)/dE of nickel, copper and Cu-Ni alloy after surface treatments. Energy of incident electron beam, 1560 eV. (1) Non-treated surface; (2) argon ion bombarded surface, 370 eV, u 1 uA*min/cm’; (3) argon ion bombarded surface, 370 eV, 2: 10 pA*min/cm2; (4) oxidation-reduction treated surface, oxidation PO% =2.3 Torr at 5OO”C, 1 min, and reduction PHI = 16 Torr at 3OO”C, 2 hr.
trast with this, after the oxidation-reduction treatment (spectrum 4), the peak at 102.5 eV was much stronger than that at 99 eV. The above Auger spectra give evidence that nickel became dense after the argon ion bombardment, while copper became dense after the oxidationreduction treatment, on the surface of Cu-Ni alloy. Catalytic activity measurements including the annealing process, however, had shown that the nature of active sites produced by the ion bombardment could be fairly analogous to those produced by the oxidation-reduction treatment. Consequently, it may be noted that the Cu-Ni ratio on the surface seems not to be dominant to the catalytic properties. Detailed observations with the Auger
316
spectroscopy annealing
study
process,
on Cu-Ni are now
being
alloys
of various
compositions,
including
made.
MASATOSHIONO*, YOSHIOTAKASU**, KATSUYA NAKAYAMA” and TOSHIROYAMASHINA**
References 1) T. Yamashina and H. E. Farnsworth, Ind. Eng. Chem. (Prod. Res. Developm.) 2 (1963) 34. 2) Y. Takasu and T. Hamashina, Shokubai (Catalyst) 10 (1968)67; to be submitted to J. Catalysis. 3) M. Ono, Y. Hayashi and K. Nakayama, in: 30th Phys. Electronics Conf., Milwaukee, March 1970. 4) L. A. Harris, J. Appl. Phys. 39 (1968) 1419.
* Electrotechnical Laboratory, Tanashi, Tokyo, Japan. ** Department of Nuclear Engineering, Hokkaido University, Sapporo, Japan.
AUGER
SPECTROSCOPY SURFACES
STUDY
RELATED
ON COPPER-NICKEL
ALLOY
TO THE CATALYSIS
Received 29 December 1970 Studies on the copper-nickel alloys have been of special interest in seeking the fundamental bases of catalysis by alloys associated with the electronic structure. We have studied the catalytic properties of copper-nickel alloys after various surface treatments, by using fairly clean surface of the alloys in sheets by means of the ultra-high vacuum apparatus. The catalytic activity of alloys was found to increase more than several tens of times by the argon ion bombardmentl) or the oxidation-reduction treatmentz). Table 1 shows several examples for catalytic activity of pure nickel and 60 wt:! Cu-Ni alloy. It is to be noted that the catalytic activity of the alloy was increased by each treatment several more tens of times than that before treatment, the activity of the alloy being much greater than that of pure nickel after the same treatment. It could be concluded that the large increases in the catalytic activity of the alloy might result from the production of lattice defects or active centers at the surface due to the ion bombardment or the oxidation-reduction treatment. In order to clarify the nature of the active sites produced by such treatments, it must be useful to determine the average Cu-Ni ratio in the surface layer which might be changed by the treatments. In the present letter, applying Auger electron spectroscopy, changes in the average Cu-Ni ratio in the surface layers of the alloy which showed rather high catalytic activity with the surface treatments have been observed. A display type LEED apparatus with four spherical grids was used as an energy analyzer for Auger electrons. The details of argon ion bombardment technique have been described elsewheres). Here, we have particularly paid attention on the Auger spectra around 100 eV in energy, since the nearly surface layers should be surely important in relation to catalytic properties. The peak structure in the higher energy region of 700 to 1000 eV was observed to be similar to the results reported by Harris4). However, lower energy spectra were more sensitive to the surface treatments. Fig. 1 represents the differentiated spectra from pure Ni, pure Cu and 60 wt% Cu-Ni alloy, showing considerable change in surface composition with the treatments. Derivative peaks for pure Ni and Cu appeared at 101 313
-_-
Oxidation-reduction PO, = 2.3 Torr 5OO”C, 1 min PHz = 16 3OO”C, 2 Torr hr
500 ev 80 A/cm2 5 min
Argon ion bombardment
Surface treatment
TABLET
Before treatment After treatment
Before treatment After treatment
Hydrogen = deuterium = exchangeg) P”uz P”D2 1.5 Torr 1OOOC
.--.-
Before treatment After treatment
.
__
Ethylene hydrogenation2) POcziip = P”Hz = I.5 Torr 100°C
Ethylene hydrogenation’) P”C,H, = PH, = 1.5Torr 40°C
Catalytic reaction
-I-
.--_.._-
_
1.0 0.18
3.2
1.o
-__.
I.0 2.1
Nickel
Relative catalytic activity
Catalytic properties of Ni and 60 wt “/oCu-Ni alloy with surface treatments
_
._
0.04 20.7
0.12 19.2
0.31 27.4
---
Cu-Ni alloy
AUGERSPECTROSCOPYSTUDYON
and 105 eV, respectively,
as shown
in
Cu-Ni
315
ALLOY
fig. 1. The electron
energies
of these
peaks were found not to be changed by any treatment. In the spectra from the alloy surfaces, on the other hand, various peak shapes were obtained for the treatments, as seen in spectrum 1 to 4. In the case of non-treatment, spectrum 1, a couple of positive peaks at 99 and 102.5 eV, corresponding to Ni and Cu positive peaks, respectively, were observed. After the ion bombardment, as in spectra 2 and 3, the positive peak at 99 eV (Ni) became to be relatively strong and the other at 102.5 eV (Cu) to disappear. In con-
90
100 Electron
110 Energy
(eV)
Fig. 1. Auger spectra, dN(E)/dE of nickel, copper and Cu-Ni alloy after surface treatments. Energy of incident electron beam, 1560 eV. (1) Non-treated surface; (2) argon ion bombarded surface, 370 eV, u 1 uA*min/cm’; (3) argon ion bombarded surface, 370 eV, 2: 10 pA*min/cm2; (4) oxidation-reduction treated surface, oxidation PO% =2.3 Torr at 5OO”C, 1 min, and reduction PHI = 16 Torr at 3OO”C, 2 hr.
trast with this, after the oxidation-reduction treatment (spectrum 4), the peak at 102.5 eV was much stronger than that at 99 eV. The above Auger spectra give evidence that nickel became dense after the argon ion bombardment, while copper became dense after the oxidationreduction treatment, on the surface of Cu-Ni alloy. Catalytic activity measurements including the annealing process, however, had shown that the nature of active sites produced by the ion bombardment could be fairly analogous to those produced by the oxidation-reduction treatment. Consequently, it may be noted that the Cu-Ni ratio on the surface seems not to be dominant to the catalytic properties. Detailed observations with the Auger
316
spectroscopy annealing
study
process,
on Cu-Ni are now
being
alloys
of various
compositions,
including
made.
MASATOSHIONO*, YOSHIOTAKASU**, KATSUYA NAKAYAMA” and TOSHIROYAMASHINA**
References 1) T. Yamashina and H. E. Farnsworth, Ind. Eng. Chem. (Prod. Res. Developm.) 2 (1963) 34. 2) Y. Takasu and T. Hamashina, Shokubai (Catalyst) 10 (1968)67; to be submitted to J. Catalysis. 3) M. Ono, Y. Hayashi and K. Nakayama, in: 30th Phys. Electronics Conf., Milwaukee, March 1970. 4) L. A. Harris, J. Appl. Phys. 39 (1968) 1419.
* Electrotechnical Laboratory, Tanashi, Tokyo, Japan. ** Department of Nuclear Engineering, Hokkaido University, Sapporo, Japan.