Catalyst – solid sorbent – or support therefor: product or process – Zeolite or clay – including gallium analogs – And additional al or si containing component
Patent
1991-07-19
1993-10-19
McFarlane, Anthony
Catalyst, solid sorbent, or support therefor: product or process
Zeolite or clay, including gallium analogs
And additional al or si containing component
4233291, 4232392, B01J 2906
Patent
active
052545156
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a catalyst for the removal of nitrogen oxides (which will hereinafter be referred to as "NOx") from a waste gas containing NOx, in particular, a catalyst for directly decomposing NOx, and to a method of purifying a gas containing NOx, in particular, a gas containing NOx, CO and hydrocarbons (which will hereinafter be referred to as "HC").
TECHNICAL BACKGROUND
Since NOx in a combustion waste gas exhausted from industrial plants, cars, etc. is a material causing photochemical smog, development of a method of removing it is an important and urgent social problem from the standpoint of protecting the environment. It is particularly difficult to remove NO of NOx gases and various methods have been proposed to solve this problem up to the present time. For example, a catalytic reduction method has been proposed and developed, as an effective means, but this method needs a reducing agent such as ammonia, hydrogen, carbon monoxide, etc. and a special apparatus for recovering or decomposing the unreacted reducing agent. On the other hand, a catalytic decomposition method is a method comprising only passing a waste gas through a catalyst bed to decompose NOx into nitrogen and oxygen without need of a special additive. This method is very simple and accordingly, it is most preferable. According to the former studies, it is found that Pt, CuO and Co.sub.3 O.sub.4 have NO decomposing activity, but they tend to be subject to poisoning with oxygen as a decomposition product and cannot be a practical catalyst [Toshio Uchijima, "Hyomen (Surface)" Vol. 18, No. 3 (1980), page 132].
Furthermore, harmful materials such as NOx, CO, HC, etc. which are considered to cause photochemical smog are contained in combustion waste gases exhausted from gasoline engines of cars, diesel engines of buses, tracks, etc. and it is an important and urgent social problem to develop a method of removing them from the standpoint of protecting the environment.
For the removal of NOx in a waste gas, there are adsorption methods, oxidation and absorption methods, catalytic reduction methods and the like, but the catalytic reduction methods have been considered advantageous from the economical and technical point of view because of no need of after-treatments. This catalytic reduction method is a method comprising passing a waste gas through a catalyst bed in the presence of a reducing gas and thereby converting NOx into unharmful nitrogen, which is classified into two methods depending on the variety of the reducing agents.
That is, these methods are the so-called non-selective reduction method wherein reduction of a waste gas is carried out by adding a reducing gas such as hydrogen, carbon monoxide, hydrocarbons, etc. and contacting with a catalyst and the so-called selective reduction method wherein the reduction is carried out by adding a reducing gas such as ammonia, etc. and contacting with a catalyst. The former method has the disadvantage that the reducing agent is reacted with oxygen jointly present in the gas and then the removal reaction of NOx proceeds, resulting in need of the reducing agent in a large amount, but in a case where a waste gas such as exhausted from internal combustion engines of cars previously contains a reducing agent such as carbon monoxide, hydrocarbons, etc. in an amount of at least equimolar to oxygen, the non-selective reduction method is more advantageous for removing NOx in the waste gas. As a catalyst for the removal of NOx in waste gases from cars, it is preferable to use one for the non-selective reduction reaction.
When no catalyst is used, a waste gas from a car has a gas composition as shown in FIG. 1, and when a three way catalyst capable of simultaneously removing NOx, CO and HC is used, the gas composition is as shown in FIG. 2, and the three components of NOx, CO and HC are removed approximately at the theoretical fuel ratio. The engine combustion waste gas at the theoretical air fuel ratio has the following composition:
The chemical reactions, in whic
REFERENCES:
patent: 4735927 (1988-04-01), Gerdes et al.
patent: 4845063 (1989-07-01), Chu
patent: 5059567 (1991-10-01), Linsten et al.
patent: 5098687 (1992-03-01), Skeels et al.
McFarlane Anthony
Mitsubishi Jukogyo Kabushiki Kaisha
LandOfFree
Catalyst for decomposing nitrogen oxides and a method of purifyi does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Catalyst for decomposing nitrogen oxides and a method of purifyi, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Catalyst for decomposing nitrogen oxides and a method of purifyi will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1351488