Note 1 to entry: A microreactor, which has a chamber-like shape and is on the micrometre scale, can be one of the processing units in a chemical process. The feature of microreactors is that temperature gradients, pressure gradients and concentration gradients increase as scale is diminished, which increases thermal conductivity, mass transport and diffusion. For instance, when the size is reduced to 1/100, molecular diffusion time drops to 1/10 000. Other potential advantages of a microreactor include better control of reaction conditions, improved safety, and improved portability. The better control results from the precise controllability of the temperature due to the high surface-to-volume ratio of the reactor. The manufacturing processes, materials and shapes of the microreactor vary with the applications.