An experimental investigation in a tube wall reactor with catalyst-coated inner wall is presented. Yields of formaldehyde of more than 70% can be obtained in the selective methanol dehydrogenation over alkalialuminate. Models for the reactor and the system of most important homogeneous reactions are derived. Different models describing the catalytic action are proposed. The results can only be explained by a new type of catalytic reaction, not described so far in the literature. Reducing gases like hydrogen and methanol lead to a volatilization of material from alkalialuminate which apparently catalyzes the dehydrogenation in the gas phase. Calculations and experimental evidence lead to the conclusion that this material should be sodium atoms. These are engaged in the homogeneous radical chain reaction by regulating the concentration of hydrogen atoms.