1. Field of the Invention
The present invention relates to a smoking article comprising a carbon monoxide reducing agent and a method of manufacturing the same, and a method of manufacturing the carbon monoxide reducing agent.
2. Description of the Related Art
Carbon monoxide that is generated during combustion of a smoking article is a substance that is preferable to be removed. Conventionally, attempts to reduce carbon monoxide included in mainstream smoke that is generated during smoking or in sidestream smoke during natural combustion have been done by incorporating a catalyst, an oxidant, an adsorbent and the like into a tobacco filler, a tobacco wrapping paper, a filter and the like.
For example, Jpn. PCT National Publication No. 2008-502343 discloses that silver oxide is used as a catalyst for oxidizing carbon monoxide. Jpn. PCT National Publication No. 2007-527782 and Jpn. PCT National Publication No. 2007-527698 disclose a catalyst comprising metal particles and/or a metal oxide of a nanoscale carried on a fibrous carrier or a high-surface area carrier. Jpn. PCT National Publication No. 2005-527205 discloses an oxyhydroxide compound that acts as an oxidizing agent for converting carbon monoxide to carbon dioxide, and exemplifies an oxyhydroxide compound of a transition metal and the like.
However, use of a large amount of a noble metal or a transition metal as a metal causes increase in the manufacture cost of a catalyst. Furthermore, use of nanoscale particles may cause problems of difficult handling in the manufacture of smoking articles, increase in costs for pulverization, and the like. On the other hand, milliscale particles having a large particle size are difficult to be included into or carried by a smoking article in the manufacture.
Meanwhile, Jpn. Pat. Appln. KOKAI Publication No. 2006-122793 discloses a catalyst including a composite oxide comprising calcium and aluminum as main components and also comprising iron as a catalyst for a shift reaction of water gas. In that publication, a catalyst comprising a composite oxide comprising calcium and aluminum (calcium aluminate) as a main component is manufactured by manufacturing a layered double hydroxide including calcium and aluminum in an alkali aqueous solution in advance, and sintering the product by heating.
It is known that calcium aluminate generally causes a hydration reaction when contacting with water and causes aggregation and crystal breakup. Since the catalyst in Jpn. Pat. Appln. KOKAI Publication No. 2006-122793 has a large BET specific surface area of 20 m2/g or more, it has a very large contact surface area with water, and thus a hydration reaction proceeds rapidly from the surfaces of the catalyst particles and causes breakup of the crystal structure or coagulation of the composite oxide. As a result, the catalyst particles are deactivated within a short time period.