[SWB123]

I have a very simple but apparently quite involved question. That being: HOW does a Catalyst (in this case ash) accomplish the task of being a "Catalyst" when it comes to the experiment of burning a sugar cube?

I have 'Googled' this question and Google comes up blank when asked 'HOW' this Catalyst works. The closest any of the choices came was to offer up a long chemical formula for what the reaction entailed. But that is a 'far cry' from what I asked. I want an english sentence explaining the details of 'HOW' it does its thing!

[Borek]

I haven't seen any good explanation. My bet is that the problem here is that it is not a simple chemistry, but rather some combination of chemistry and physics - things like wicking of the melted sugar, presence of a solid that helps in evaporation of the molecules  (think in terms of a boiling stone) and so on. These things can get quite convoluted and it can be impossible to separate them, as what we observe is only a final effect.

[Corribus]

Were I forced to make a vague guess, I would say that trace metals left in ash (a kind of poor-man's activated carbon) help catalyze formation reactive oxygen species that are able to more rapidly oxidize sugar.

Even in highly purified catalysts, though, mechanisms can be highly complex and poorly understood.

[Enthalpy]

Would someone try with sugar wrapped in glass fibre? I have nothing at hand here.
Glass fibre made a good wick for wax last time I tried. If sugar burns then, it would be a hint in favour of a wick.
Though, a very thin layer of ash suffices already, so I would favour catalytic action.

[Arkcon]

This is an old, old chestnut, that I'd heard when I was a kid, reading kid's chemistry books published in the 1950's: A sugar cube can't burn without a dot of cigarette ash as a catalyst.

The ash is likely completely burnt, so it can't oxidize more, so it can't be a chemical reaction.  As Enthalpy: said, if its a physical wick to should be workable with anything -- glass fiber, asbestos fibers, expanded vermiculite, perlite, diatomaceous earth, and anything else you can name.

The real problem is the process is complete bunk -- a kid's chemistry book written in the 1970's said to just light a sugar cube, and it lights.  I guess they wanted to correct the "catalyst" error.  Without actually mentioning it.  I've burned sugar all the time, just scoop some onto the gas hob and *Woosh*.

And where, in this day and age, are you gonna even find cigarette ash, or, heck, sugar cubes, even.

Like Corribus: said, what exactly is the effect of a catalyst, really?  Example, hydrogen reactions are often catalyzed by platinum metals.   The way that works is, the electron shell of the hydrogen interacts with the platinum metals electron "sea".  And I'm like, so don't all metals have there electrons de-localized, why then is platinum preferable?

The answer given is that platinum may form a better surface, free of oxidation, and may interact weaker than other metals, so the hydrogen if also free to work.  But it still seems that every metal should catalyze every gaseous reaction by electron cloud interaction. 

[Enthalpy]

Cigarette ash isn't the only one. I did it with cotton ash, from nice clean white cotton meant for use on the skin. It leaves very little ash but this sufficed.

My sugar was a powder, not cubes, but I couldn't light it within reasonable time.

Less clear: I had the sugar powder on a layer of cotton and I lit the cotton, which had all the time to heat the (thick) sugar powder, so the action wasn't necessarily a catalysis nor by ash. Also, with cotton ash and still unburned cotton below, the sugar powder burned at its top too, hence without direct contact with the ash.

Paper (or the better aerated cardboard) could be worth trying too, as it contains cellulose like cotton and cigarettes do.

My vague impression: when sugar is heated, the evolved gas contains water, while much carbon remains at the solid. This must hamper the combustion of sugar, which would otherwise have all the ingredient of a good fuel, notably vapour pressure at an accessible temperature. So a catalyst could orient the decomposition towards burnable volatiles (alcohols, aldehydes, monoxide...) more than water.