Scott, if I'm reading him aright, it sounds to me like he wants to use the chemical energy like rocket fuel to power his temporal journey to the past, but power it remotely such that the energy is all directed into the time travel trip but the waste product remains in its location in what will then be the future.
I had similar thoughts earlier, but I was thrown off by his statement that he had no intention of effecting a change in the matter. Now it appears he intends to draw the affected matter back into the past with him, and also that the matter be inert when he arrives. Actually, scratch that; I guess he's suggesting that that's one way it could work, but the way he would prefer it to work is that the matter to become inert but not to make the trip.
What I find more difficult is the notion of using the energy for time travel, since psionic time travel doesn't use much energy at all and he is not attempting technological time travel.
Perhaps it doesn't, but he imagines it does, and in connection with that I observe two things: first, that once you get into the tip-top bias levels in the psi area, the imagination becomes very important to both the effect and the execution; and second, that it quite possible for Maxx to be mistaken about how he is doing what he does (or even about what he is doing).
Thus, he begins with his surroundings transformed into a mixture of two volatile substances, ready to explode.
Next, he travels back in time, and his transmuted, volatile surroundings become inert (for no reason apparent to the casual observer), reaching such a state as it would have been in had it been allowed to explode (and left for several hours thereafter to cool).
Finally, he arrives in the past.
I believe that to be an adequate description of the results Maxx intends. There is no reason that is has to happen for the reasons that he imagines it to happen. He imagines he cannot travel back in time without an energy source, so he alters reality (preventing an explosion) and imagines that the change in potential energy has provided him with the power necessary to travel through time; armed with this confidence, he proceeds to travel through time.
I think I'll combine the P14@7 Transmute Matter with the P14@10 Time Travel into a single skill, but allow that the explosive target material acts as a mental focus for the time travel aspect, providing a +10 sit-mod which cancels out the -10 combination penalty. +10 for an extra minute's concentration, - some value for quantity of material and difficulty of the job; +2 because his character bias is P15@2, +15 for world bias, +20 for his BRA comes to less than or equal to 47%, the roll is 63, failed.
Just as well. I never asked how far back he expected to travel, and I'm not sure whether or not his body would have come with him. I'm thinking so?