  Up to now, the methods available for measuring the rate constants of
reactions taking place on heterogeneous catalysts require that the catalyst be
stable over long measurement times. But catalyst are often non-stationary, they
may become activated under reaction conditions or become poisoned through use.
It is therefore desirable to develop methods with high data acquisition rates
for kinetics, so that transient rates can be measured on non-stationary
catalysts. In this work, we present velocity resolved kinetics using high
repetition rate pulsed laser ionization and high-speed ion imaging detection.
The reaction is initiated by molecular beam pulses incident at the surface and
the product formation rate is observed by a sequence of laser pulses at a high
repetition rate. Ion imaging provides the desorbing product flux (reaction
rate) as a function of reaction time for each laser pulse. We demonstrate the
method using a 10 Hz pulsed CO molecular beam pulse train to initiate CO
desorption from Pd(332) - desorbing CO is detected every millisecond by
non-resonant multiphoton ionization using a 1-kHz Ti:Sapphire laser. This
approach overcomes the time-consuming scanning of the delay between CO and
laser pulses needed in past experiments and delivers a data acquisition rate
that is 10-1000 times higher. We also apply this method to CO oxidation on
Pd(332) - we record kinetic traces of CO$_2$ formation while a CO beam titrates
oxygen atoms from an O-saturated surface. This provides the reaction rate as a
function of O-coverage in a single experiment. We exploit this to produce
controlled yet inhomogeneously mixed reactant samples for measurements of
reaction rates under diffusion-controlled conditions.
