This paper presents a stochastic resonance occurring in a chemical reaction Pt(100)/NO+CO. The results were from numerical simulation of the nonlinear kinetic behavior of a three-variable reaction model obtained from the law of mass actions. The model exhibits a special region in the bifurcation scheme, where a stable node coexists with a stable limit cycle. When one of the control parameters is perturbed by a weak, low frequency periodic signal riding on a suitable external noisy background, transitions between the steady state and oscillatory state may become regular unexpectedly, and signal to noise ratio is thus enhanced at the signal frequency in the Fourier transform power spectrum of the time series output. That refers to stochastic resonance, in which the noise may play a constructive role in the detection of weak signals. The findings may suggest a new method to develop chemical sensitive devices in the field of applications. The paper also discusses the conditions of occurrence of stochastic resonance, and studies the laws it follows.