Hello everyone and welcome to this
week's video! Today I'm going to be talking about catalytic converters, more specifically three-way catalytic
converters. And what three-way means is it's trying to eliminate Nitrogen Oxide
emissions, Carbon Monoxide emissions, and Hydrocarbon emissions; or, in other words,
unburned fuels. So, the way it does this inside of a
catalytic converter, you've got these two blocks and one is a
reduction catalyst, and the other is an oxidation catalyst, and the the reduction
catalyst is made up of platinum and rhodium, and the oxidation catalyst is
made up of platinum and palladium. So what happens is, you've got... from
combustion you've got CO2, y'got carbon monoxide, you've got nitrogen oxides, got oxygen
water, and unburned fuel, all coming into this catalytic converter. now the first step it goes through, is
this reduction catalyst, platinum rhodium and what happens is, you're trying to
eliminate the nitrogen oxides. So the nitrogen oxide will come into
this catalyst and, so inside of this it's just a bunch of tiny little ducts, little
micro ducts and there's thousands of them, and that's what the air is passing
through so you're trying to maximize surface area with that design. So the nitrogen dioxide will come in and
the nitrogen bond with the oxygen isn't as strong as its bond with the catalyst, so
once the bond with catalyst so it will bond the catalyst and when it does that
it'll weaken its bond with the two oxygens. So the two oxygens will separate
off, and they may go off, or they can join together. But eventually these two
oxygens are going to find another oxygen to pair up with so that they're O2 rather than just O, which is a little more stable. So, once these nitrogens are all alone
here on this catalyst they'll move along the surface, they want to meet up with
another nitrogen, that- they prefer that bond rather than the catalyst.
So once they bond with another nitrogen, their bond with the
catalysts weaken and they split off and- and go off to the next step. And so then you're just left with
nitrogen and oxygen, which are both perfectly harmless gases in your
catalyst, the surface is ready to continue this function with other
elements and other molecules. So then after you go through the first step we've eliminated NO2 and and and NO,
and- so now we just have N2, O2, CO, CO2 H2O and our hydrocarbons. So the next step is this oxidation
catalyst, which is made of platinum and palladium. So what happens in here, is the catalyst
surface wants to bond with oxygens. So what will happen is the carbon
monoxide and the oxygen molecules will come and they'll bond with the surface. Now once the oxygen molecules bond with
the surface, they'll split up and when they split up, the bond with the carbon
monoxide is stronger than just by themselves. So they'll bond to the carbon
monoxide, they'll form carbon dioxide, and then the bottom of the catalyst is
weakened so this will go off and out the out the
catalytic converter continue on through the exhaust and then your catalyst
surface once again is free and ready to continue doing this- this function here to eliminate carbon
monoxide. So then- also within this you're trying
to get rid of these hydrocarbons and so we have these freed up oxygens we've got
hydrocarbons- if you haven't watched my video on air-fuel ratio stoichiometric air-fuel ratio, that may help. Basically your
hydrocarbons and oxygen are going to form H2O and CO2. They're going to
combust within this- react within this catalytic converter, and so they'll
be forming the harmless H2O, and then the kind of harmful CO2. So catalytic
converters do not eliminate CO2 but they do eliminate the other gases, NO2, NO, and CO. So after it's gone through this phase,
then you're just left with N2, O2, CO2 and H2O, and catalytic converters can do
this on about a 90 of percent efficient basis so they're still going to be some
of these harmful gases leftover, but about ninety percent of them it can convert and some obviously are
better than others. In catalytic converters, one thing to
note is they work best once heated up, that's how the reactions occur a little
more easily. So that's catalytic converters and their
function. If you haven't already, i would recommend watching my video on exhaust
systems, it kind of gives you the basic overview Thanks for watching!
