We present a new technique for using catalytic space to simulate space-bounded randomized algorithms.
Allocate one bit on the catalytic tape for each configuration of a randomized machine.
Simulate the machine several times.
Each time it requests a random bit, use the bit from the catalytic tape corresponding to its current configuration, and then flip the bit on the tape.
Because the bit is flipped each time, every configuration of the randomized machine will receive a 0 in the same number of simulations as it receives a 1, up to a difference of 1.
It follows that the simulation visits each configuration approximately the same number of times as it would if it used true randomness.
Finally, the catalytic tape can be restored by re-running the simulations with a small change that reverses their effect.
This yields that $\mathrm{BPL} \subseteq \mathrm{CL}$ and $\mathrm{BPL} \subseteq \mathrm{P}$, both of which were already known.

In fact, the technique has so far given no new results.
However, we believe it merits further study, because it is simple, and because it is different from all previous catalytic techniques, which, broadly speaking, fall into two categories: either attempt to compress the catalytic tape (deriving something useful when it is incompressible) or treat the tape as registers for a pre-determined sequence of mathematical operations.
Our technique is different from both, suggesting an opportunity for finding new catalytic algorithms, or for combining techniques to get stronger results.