An apparatus for the production of formaldehyde is disclosed. The apparatus comprises a cooled tubular reactor section (8, 108, 208, 308, 408, 508) having a first inlet, a first outlet and a plurality of tubes each having a first end in fluid communication with the first inlet and a second end in fluid communication with the first outlet. The plurality of tubes contain a first catalyst for the production of formaldehyde by oxidative dehydrogenation. The apparatus is characterised in that the apparatus further comprises a pre-reactor section (7, 107, 207, 307, 407, 507). The pre-reactor section (7, 107, 207, 307, 407, 507) has an inlet. The pre-reactor section (7, 107, 207, 307, 407, 507) has an outlet in fluid communication with the first inlet of the cooled tubular reactor section (8, 108, 208, 308, 408, 508). The pre-reactor section (7, 107, 207, 307, 407, 507) is configured to contain, in use, an adiabatic catalyst bed. The adiabatic catalyst bed comprises a second catalyst for the production of formaldehyde by catalytic oxidative dehydrogenation.