Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
1999-08-24
2001-07-17
Griffin, Steven P. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S185000, C502S327000, C502S335000, C208S137000
Reexamination Certificate
active
06261991
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
1. Field of the Invention
The present invention relates to an improved steam-reforming catalyst for hydrocarbons having a smaller reduction in catalyst activity.
2. Prior Art
Generally, the high activity of a catalyst is realized by finely dispersing an active component and enlarging the surface area of the active component. As is well-known, the method of finely dispersing metal particles is realized by e.g. an oxidoreduction treatment or a deposition/precipitation carrying method after the metal particles are carried by impregnation, deposition, co-precipitation, kneading, ion-exchange etc. However, even if the active component is micronized for application to a steam-reforming catalyst for hydrocarbons, the sintering of the active component is significant because the catalyst is used at high temperature. As particles of the active component become finer, sintering proceeds more rapidly, causing a rapid reduction in activity.
On one hand, it is effective to raise the effective diffusion coefficient of a catalyst by devising its pore structure in order to perform a steam-reforming reaction for hydrocarbons with a high activity of the catalyst. This is because in said reaction, the diffusion resistance upon diffusion of a reaction material and product through pores is high.
In JP Patent No. 1,894,792 and JP-B 6-83787, the present inventors proposed that the high activity of a catalyst is realized by devising the pore structure of the catalyst to raise the effective diffusion coefficient. Further, in JP-A 9-299798, they disclosed a proposal that both the mechanical strength and high activity of a catalyst are allowed to remain.
In these studies, the present inventors also examined the micronization of an active component. Generally, the high activity of a catalyst can also be realized by finely dispersing an active component and enlarging the surface area of the active component, and this also applies to the steam-reforming reaction for hydrocarbons. That is, the increase of the effective diffusion coefficient and the micronization of the active component contribute synergistically to a higher activation, but as described above, there is the problem of significant sintering of the active component in said reaction.
The highly active catalyst proposed by the present inventors could be practically used because the reduction of its activity was lower than that of conventional commercial catalysts. However, although said catalyst was practical, the reaction temperature should be increased for a short time in a reactor in order to maintain the same rate of reaction. The energy therefor is increased as the activity of the catalyst is lowered. Accordingly, from the view point of saving energy, there remains the problem of preventing the activity of the catalyst for a long time from being lowered.
PROBLEM TO BE SOLVED BY THE INVENTION
The object of the present invention is to provide an improved steam-reforming catalyst for hydrocarbons having a smaller reduction in catalyst activity.
MEANS FOR SOLVING THE PROBLEM
To lessen the reduction of the activity of a steam-reforming catalyst for hydrocarbons, the present inventors, by repeated trial and error, made extensive studies. As a result, they found that the catalyst described below hardly undergoes any activity reduction.
That is, (1) the catalyst wherein the carrier is &agr;-Al
2
O
3
or CaO—Al
2
O
3
, Ni, as the active component carried by said carrier, forms, together with the carrier, a compound composed of Ni and &agr;-Al
2
O
3
(abbreviated hereinafter to NiAl
2
O
4
) and is carried as Ni and NiAl
2
O
4
, carbon is contained in both Ni and NiAl
2
O
4
, and the grating constant of Ni and the grating constant of NiAl
2
O
4
in said catalyst are increased as compared with those of the catalyst before carbon is added, (2) the catalyst wherein the carrier is &agr;-Al
2
O
3
or CaO—Al
2
O
3
, carbon is contained in Ni as the active component carried by said carrier, and the grating constant of Ni in said catalyst is increased as compared with that of the catalyst before carbon is added, and (3) the catalyst in items (1) and (2) above wherein Ni as the active component is contained as Ni in an amount of 3 to 20 wt-%.
The present invention was made on the basis of the above-described circumstances and the above-described findings, and the object of the present invention can be achieved by the following means.
That is, the present invention provides:
(1) An improved steam-reforming catalyst for hydrocarbons, wherein the active component Ni is supported on an &agr;-Al
2
O
3
carrier, a part of said active component Ni is combined with said carrier to form a compound NiAl
2
O
4
, carbon is contained in both of said Ni and NiAl
2
O
4
components, and the grating constant of Ni and the grating constant of NiAl
2
O
4
in said catalyst are increased as compared with those of the catalyst before carbon is added to both of said components;
(2) An improved steam-reforming catalyst for hydrocarbons, wherein the active component Ni is carried by a CaO—Al
2
O
3
carrier, a part of said active component Ni is combined with said carrier to form a compound NiAl
2
O
4
, carbon is contained in both of said Ni and NiAl
2
O
4
components, and the grating constant of Ni and the grating constant of NiAl
2
O
4
in said catalyst are increased as compared with those of the catalyst before carbon is added to both of said components; and
(3) The improved steam-reforming catalyst for hydrocarbons according to item (1) or (2) above, wherein the increase of the grating constant of Ni is 0.0001 to 0.0008 nm, and the increase of the grating constant of NiAl
2
O
4
is 0.001 to 0.005 nm.
Further, the present invention provides:
(4) An improved steam-reforming catalyst for hydrocarbons, wherein the active component Ni is supported on an &agr;-Al
2
O
3
carrier, carbon is contained in said active component Ni, and the grating constant of Ni in said catalyst is increased as compared with that of the catalyst before carbon is added to said active component Ni;
(5) An improved steam-reforming catalyst for hydrocarbons, wherein the active component Ni is supported on a CaO—Al
2
O
3
carrier, carbon is contained in said active component Ni, and the grating constant of Ni in said catalyst is increased as compared with that of the catalyst before carbon is added to said active component Ni;
(6) The improved steam-reforming catalyst for hydrocarbons according to item (4) or (5) above, wherein the increase of the grating constant of Ni is 0.0001 to 0.0008 nm; and
(7) The improved steam-reforming catalyst for hydrocarbons according to any one of items (1) to (6) above, wherein the active component is contained as Ni in an amount of 3 to 20 wt-%.
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, suitable hydrocarbons to be reformed with steam are C
1
methane to C
8
hydrocarbons and their compounds.
The carrier will be described. In the present invention, typical components of the carrier include, but are not limited to, &agr;-Al
2
O
3
and CaO—Al
2
O
3
. The carrier has distributed pores, and there is no limit to the shape of pore distribution therein. For example, the carriers disclosed by the applicant in JP Patent No. 1894792, JP-B 6-83787, JP-A 9-299798 etc. can naturally be included in the present invention.
Hereinafter, the active component of the catalyst is described. The active component as the subject of the present invention is Ni.
As the active component, Ni is contained in a content of 3 to 20 wt-% in the catalyst. When the content thereof is less than 3 wt-%, the activity of the catalyst may be low. When the content thereof exceeds 20 wt-%, the catalyst has sufficient sintering resistance, but the activity of the catalyst may not be increased adequately, and thus the Ni content of 3 to 20 wt-% in the catalyst suffices as the concentration of the active component.
There is no adverse effect on the activity or activity reduction of the catalyst of the present invention, even if alkali metals such as K, alkaline earth
Izawa Yasuhiro
Numaguchi Toru
Flynn ,Thiel, Boutell & Tanis, P.C.
Griffin Steven P.
Nguyen Cam N.
Toyo Engineering Corporation
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