Hydrogen reactions with catalysts I have a question about reactions involving hydrogen using catalysts. I'm a layman, so forgive me if my questions seem elementary.

Reacting hydrogen plus oxygen and a flame reacts, unleashing energy (in the form of an explosion) and creating water.

My questions:


Why does it need a "flame or spark "? Is there something unique
about the fire that causes the reaction? Or is it merely the heat of the flame? In other words, if you put hydrogen and oxygen in, say, a
pressurized vessel and added energy in the form of heat (but not a
flame) would it still react and create water? Would it do it without an explosion?
I understand catalysts "speed up" the reaction, or put another way,
reduces the amount of energy required to cause it. I've read that in
this particular reaction ($\ce{H2 + O2}$) copper works as a
catalyst. Is there a way to determine by looking at the chemical
formulas if other catalysts would work as well or better or is it
just trial and error? For example, could you tell if silver would
also act as a catalyst just by looking at the formula? Or would you
need to actually add silver and see for yourself?
When a catalyst is used, is it inexhaustible or does it get "used
up"? If you were using copper to react these two, could you use it forever? If not, is there a way to "recharge" the catalyst?


Thanks in advance, I'm trying to learn about this particular reaction for a project I'm working on ($\ce{H2 + O2}$) but without a formal science background, some of the scientific papers I'm reading are a little hard to grasp.
Adding a bit of information for your question a). The reactin we are looking at is:

$$\ce{2 H2 + O2 -&gt; H2O}$$ 

As you can clearly see, the final product water has one oxygen atom for 2 hydrogen atoms, while in the beginning, we only had diatomic molecules. This means that during the reaction, at least one fo the diatomics had to break to single atoms. In this case, this happens with the reaction:

$$\ce{H2 -&gt; 2H^.}$$

From this step, we have a nice reaction scheme called a radical chain reaction. However, we first need to break the $\ce{H-H}$ bond somehow, and this is what flame is doing. If you break a significant amount, then you don't need to provide flame anymore, the reaction is self-supporting — the flame is ignited.

Now, a catalyst is doing exactly this. Many metals, including copper, can adsorb hydrogen molecules to the surface, and this also results in breaking the $\ce{H-H}$ bond — so the explosion can start this way too.