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There’s nothing new under the sun – a brief look at historical climate change patents – Part 6: Catalytic Converters


Catalytic converters are good for the environment. Catalytic converters are also bad for the environment; it depends what criteria you choose to assess good and bad. One thing we know is that patent applications have been filed in this technology for more than 100 years.

Catalytic converters are the silent hero of your car’s exhaust system, taking all of the unburnt hydrocarbons, carbon monoxide, nitric oxide and nitrogen dioxide and converting it into carbon dioxide and water.  This totally inert piece of technology prevents deadly levels of carbon monoxide entering the atmosphere, and stops nitric oxide and nitrogen dioxide being blown up into the sky and falling as acid rain or causing smog.  Without them then, a climate crisis  would be in full swing and global leaders would have to meet every year to discuss what they think they will do about the problem – so why is this still happening?

Catalytic converters at their most basic oxidise carbon monoxide into carbon dioxide, and oxidise unburnt hydrocarbons into carbon dioxide and water.  More modern converters also reduce nitrogen dioxide and nitric oxide into nitrogen, carbon dioxide and water.

To understand why catalytic converters haven’t solved all of the worlds ills, it is helpful to know that they were invented long before anyone believed carbon dioxide is bad for the environment.  Indeed as early as 1909 a patent application, FR 402173, was filed by a Michel Frenkel from France for a catalytic converter.  It used a clay honey comb structure coated with platinum, and had a fan to blow air into the converter ensure oxygen was present for the oxidation reactions.  Sadly, as the effects of air pollution weren’t readily noticeable, nobody really thought that Frenkel’s invention was particularly necessary.

In the 1930’s an inventor called Eugene Houdry, also from France, tried again to solve this problem.  He filed a patent application, US 2742437, which used an inert metal structure with a catalyst impregnated film covering the structure, over which exhaust gases could flow to reduce the quantity of carbon monoxide in the air.  As It was now clear (or indeed very hazy) that smog originated around roadways and led to a lot of coughing and spluttering, Houdry managed to form a very successful business selling his catalytic converters in the United States.

To deal with the nitrogen oxides in Exhaust gases, in 1971 John J Mooney and his team at Engelhard came up with the first “monolithic” catalytic converter which dealt with both oxidation of carbons and also the reduction of nitrogen oxides to nitrogen, carbon dioxide and water. Prior to this a two stage catalytic converter was used which required a fan to provide enough oxygen to the second, nitrogen reducing stage.  Their patent US 3896616 shows their invention below.

To provide a carbon atom or CO molecule to remove the oxygen from the nitrogen oxides, a “rich” engine mixture is used, meaning that to avoid nitrogen oxides entering the atmosphere, the engine must use more fuel than it otherwise would, and produce more carbon dioxide than it otherwise would. In Mooney’s patent above you can see that fuel is directly added to the nitrogen converter (17).

It was not thought that carbon dioxide could have any effect on the environment until the late 1950s, although some people had been shouting this since the late 1800s.  Monsieur Houdry, certainly didn’t think it was a problem, as evidenced in his granted US patent US 2,776,875, where he describes carbon dioxide as “a harmless constituent” in his new pelletized catalytic converter.

Carbon dioxide concentration in the atmosphere is now the metric by which we measure the advance of human caused climate change. 

Furthermore, It has been identified that nitrous oxide, a by-product of the nitrogen reduction catalytic converter, although produced in small amounts, is over 300 times more effective at trapping heat than carbon dioxide. 

So while catalytic converters are good preventing pollutants from entering our airways, consensus seems to have turned to  the opinion that catalytic converters are bad for climate change.  Advances in materials, such as the use of copper/cadmium converters, rather than traditional platinum, can prevent more nitrous oxide leaving the exhaust, however it doesn’t seem that carbon dioxide emissions can prevented with current technology.  There is room for improvement and innovation in this technology – speak to one of the attorneys at Reddie and Grose if you know how to solve this problem.

This article is for general information only. Its content is not a statement of the law on any subject and does not constitute advice. Please contact Reddie & Grose LLP for advice before taking any action in reliance on it.

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