Photon Factory Activity Report 2004 #22 Part B (2005)
Surface and Interface

9A, 7C, 1B/2003G067

Effect of calcination and reduction of Ni/Al2O3 catalysts analyzed by XAFS
M.Carmen ROMÁN*1, Jerónimo JUAN1, M.José ILLÁN1, Hiromi YAMASHITA2
1
Department of Inorganic Chemistry, University of Alicante, 03080 Alicante, Spain
2
Department of Material Science and Processing. Graduate School of Engineering. Osaka University
2-1 Yamada-oka, Suita, Osaka, 565-871 Japan

Experimental
A Ni/Al2O3 catalyst was prepared by excess solution
impregnation using a pelletized γ-Al2O3 support and an
aqueous solution of Ni(NO3)2.6H2O of the appropriate
concentration to obtain about 10 wt% Ni. Activation
treatments were: i) Calcination: in air at 773K, 12 h, andii) Reduction: in H2 flow at 773K for 2h.
XAFS measurements were done in the following samples:
CR: calcined and reduced, both fresh and used in reaction
R: only reduced, both fresh and used in reaction
NT: with no treatment, only used in reaction
Reaction conditions: 0.18 g catalyst, mixture CH4:CO2(50:50), 60 ml/min, 973K, 6h.
The Ni K-edge absorption spectra were recorded in thetransmission mode at room temperature, in a range ofphoton energy extending from 8080 to 9375 eV. A FT3transform was performed on the k -weighted EXAFS-1
oscillations over the range 3-12 Å .
Results and discussion
Figure 1 shows the FT-EXAFS data obtained for the Ni/
Al2O3 catalysts CR and R. The signals corresponding toNiO and Ni foil have been also included.
These results show that calcination previous to thereduction treatment has an important effect in the extentof the reduced state, being clearly higher for the CR
sample. This was also verified by the XANES data.
As already reported [1,2], the catalysts become furtherreduced under reaction conditions. It was even suggested
that probably there is no need for a reduction treatment[2]. In fact, catalysts CR, R and NT give a similar activity
for CO2 methane reforming in the conditions indicatedabove. However, they differ in selectivity as the amountof coke deposited is not the same (180, 140 and 280 mg/g,

respectively for catalysts CR, R and NT after 6h reactiontime).
60NiO
sample Rsample CR
Ni foilI(a.u.)

504030
20
1000Users' Report

4R(A)68The FT-EXAFS spectra obtained for the used catalysts
are shown in Figure 2.
60
sample R
sample NT
sample CR
Ni foil

50403020100024R(A)68Figure 2. FT-EXAFS of catalyst used in the CO2 methane
reforming (973K, 6h).
According to these data, the modification of thecatalysts under reaction conditions is strongly influenced
by the pretreatments. Used catalysts CR and R have Ni
particles with a very different structure, being for the firstone more similar to that of metallic nickel. On the otherhand, it is striking that the used catalyst NT shows, likesample CR, Ni particles with a defined structure. Theseresults reveal the important effect of the conditions of theheat treatment and the nature of the reducing atmosphere.
These data also confirm the well known structuresensitivity of the coke deposition reaction.
References[1] J. Juan et al., Appl. Catal. 264 (2004) 169-174.
[2] M.C. Román et al., PF user’s report, 2003
* mcroman@ua.es90

2Figure 1. FT-EXAFS of fresh catalysts.

I(a.u.)

Introduction
Ni/Al2O3 catalysts are under investigation in theirapplication for the CO2 methane reforming. Their maindrawback is a poor stability caused, mainly, by a highcoking rate. Preparation of the mentioned catalysts is
usually done by impregnation, followed by calcination
and reduction steps. Current investigations show a minor
effect of the activation treatments in the catalytic activityof the samples. In this study we analyze the effect ofcalcination and reduction treatments of a Ni/Al2O3
catalyst in the state of Ni in order to find a relation
between catalytic properties and structure.