Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Patent
1997-11-10
2000-04-04
Wood, Elizabeth D.
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
502329, 502331, B01J 2306, B01J 2310, B01J 2372
Patent
active
060461292
DESCRIPTION:
BRIEF SUMMARY
FILED OF INVENTION
This invention relates to a catalyst and more specifically to a catalyst for purification of industrial and automotive vehicle exhaust gas.
BACKGROUND OF THE INVENTION
In the recent years, as the awareness of environmental protection grew, many countries started regulating industrial and automobile emissions through legislation, prodding the industry and academia to come up with an environmentally friendly catalyst. As the number of automobiles multiplied, automobile emission has become a major source of air pollution. In the U.S. automobile emission accounts for nearly 60% of air pollution, whereas industrial exhaust accounts for 17%. Automobile exhaust fumes contain carbon monoxide (CO), unburned hydrogen carbonate (HC), and nitrogen oxides (NO.sub.x) which is mainly NO and NO.sub.2. Nitrogen oxide is well known for damaging ozone (O.sub.3) in our atmosphere. The O.sub.3 layer filters out much of the ultraviolet radiation; however, damage to the O.sub.3 layer results, which thereby exposes the earth surface to an excess amount of ultraviolet which is responsible for causing skin cancer.
Most of the catalysts available today are designed to reduce the amount of carbon monoxide (CO) and hydrogen carbonate (HC) in automotive vehicle exhaust gas. However, there is much demand for a catalyst that can simultaneously treat CO, HC and NO.sub.x. The conversion of CO and HC is an oxidizing reaction, while the conversion of NO.sub.x to inert N.sub.2 is a reduction reaction. Therefore, a catalyst that can treat all three ingredients must be an oxidizing agent as well as a reductive agent. Moreover, such a catalyst is efficient under a small window of operating conditions of the automobile engine, e.g. air/fuel ratio should be kept at a strict stoichiometric relation. Leaded gasoline which is now used in some countries could poison automobile exhaust catalysts. The sulfide in exhaust gases can also poison catalyst. Western countries (e.g. the U.S.) has enacted the automobile emission standard which stipulated lead-free gasoline as standard motor fuel.
A description of the catalyst for purification of automobile exhaust gases in which noble metals e.g. Pd, Pt, Ru and rare earth metals are used as the active ingredients has been reported in the literature. However, these catalysts are undoubtedly more costly. Other catalysts using non-noble metals as the active ingredients may also be found in the literature. But the common problem for these catalysts is low conversion rate, especially at low temperature, and poor durability. Some catalysts should be equipped with oxygen sensor and heating unit, the active ingredients and the proportion thereof differ greatly different from those of present invention.
Chinese patent application No. 85109694.8 discloses a nonmetal honeycomb-shaped combustion catalyst which applied double-carrier and oxide of Cu, V, Mn, Co, Ni, or oxide/mixture of several elements above mentioned, and adopted rare-earth elements, e.g. La, Ce, Pr, Sm, Nd, Yt as active ingredients.
Chinese patent application No. 98105063.9 discloses a catalyst similar to Chinese Patent No. 85109894.8. that consists of composite carrier made from honeycomb-shaped ceramics materials coated with aluminum oxide, and active ingredients which are one or multi oxides (or mixture made of these oxides) of nonnoble metals e.g. Zr, Co, Ni, Mn, Cu, Cr and the oxide of a rare-earth element. But the active oxides are reduced by hydrogen, carbon monoxide, or hydrocarbon oxides during the preparation process in which a portion of the active oxides of the metal elements are converted to metal elements. The catalyst calcine technology is not acceptable at 700-1100.degree. C. As the temperature is increased to 865.degree. C., .gamma.-Al.sub.2 O.sub.3, becomes crystalline and shows low activity and stability. Since .gamma.-Al.sub.2 O.sub.3 is amorphous (indefinite) at 200-600.degree. C. with high activity and dispersion. When the temperature is up to 1100.degree. C., .gamma.-Al.sub.2 O.sub.3 becomes non-active .alpha.-A
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Duan Fengying
Duan Fuxun
Duan Junwei
Duan Zhongshan
Lu Yongnian
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