NOVELTY - A gas-solid phase exothermic catalytic reactor with low temperature difference comprises a shell (P), partition (H), cold-tube internals (Cb), holder (S) and porous plate (R).    USE - The reactor is useful in chemical engineering particularly for synthesis of methanol and alkanes, and also in methylamine, methane and dimethyl ether production.    ADVANTAGE - Such reactor has low temperature difference across the catalyst layer, high catalytic activity, simple and reliable structure, and good operating performance at low investment cost.    DETAILED DESCRIPTION - A gas-solid phase exothermic catalytic reactor with low temperature difference comprises a shell (P), partition (H), cold-tube internals (Cb), holder (S) and porous plate (R). The shell (P) is a pressure-resistant vessel with a gas-inlet (1) at top and a gas-outlet (2) at the bottom both with flange seal-heads. The partition (H) divides such reactor into two sections of upper and lower gas chambers the latter of which is filled with a catalyst layer (K). The end-holder (S) supports the cold-tube internals (Cb), and the end-porous plate (R) holds the catalyst layer outside the cold-tube internals. The gas-fed-in tube (a) of the cold-tube internals passes through the partition (H) and is sealed with the removable stuffing box, the cold-tube internals with gas-inlet tube (a) and circular tube (c), or upper and lower circular tubes (c, d), cold-tube (b) which is a U-shape tube, circular tubes connected to (a) and (b) at the top and bottom. Synthetic feedstock is supplied from the shell (P) through the inlet (1) via a gas-inlet tube (a) to the circular tube (c) for distribution to the various cold tubes (b) flowing from top to bottom, during which the cold gas in the cold-tube internals exchanges heat with the reaction gas in the catalyst layer (K) outside the cold-tube internals in concurrent before leaving the reactor from the outlet (2).    DESCRIPTION OF DRAWING(S) - Structure of a synthesis tower with cold tube (b) in the reactor being in U shape. (Drawing includes non-English language text).    Gas-inlet (1)    gas-outlet (2)    shell (P)    partition (H)    cold-tube internals (Cb)    holder (S)    porous plate (R)    catalyst layer (K)    gas-fed-in tube (a)    cold tube (b)    circular tube (c)