Described herein are expandable center arrangements for use in a tubular reactor, such as a reformer, for enhancing heat transfer and reactor efficiency. The expandable center arrangement can include a cone being expandable in the radial direction and an expansion weight for promoting expansion of the cone. The cone and expansion weight can be slidably arranged on a center support. Expansion of the cones in the radial direction forces reactor components radially outward to an outer tube that houses the reactor components and expandable center arrangement. Expansion of reactor components towards the outer tube promotes heat for carrying out catalytic reactions.

The present invention relates to a catalytic system comprising at least two catalytic zones of which at least one zone exclusively contains one or more noble metals selected from the group consisting of Rhodium, Ruthenium, Iridium, Palladium and Platinum and at least another zone contains Nickel, said catalytic system characterized in that at least one zone exclusively containing noble metals selected from the group consisting of Rhodium, Ruthenium, Iridium, Palladium and Platinum is always distinct but in contact with at least one zone containing Nickel.

One or more metals selected from the group consisting of Rhodium, Ruthenium, Iridium, Palladium and Platinum are possibly added to the catalytic zone or zones comprising Nickel.

The present invention relates to a catalytic system comprising at least two catalytic zones of which at least one zone exclusively contains one or more noble metals selected from the group consisting of Rhodium, Ruthenium, Iridium, Palladium and Platinum and at least another zone contains Nickel, said catalytic system characterized in that at least one zone exclusively containing noble metals selected from the group consisting of Rhodium, Ruthenium, Iridium, Palladium and Platinum is always distinct but in contact with at least one zone containing Nickel. One or more metals selected from the group consisting of Rhodium, Ruthenium, Iridium, Palladium and Platinum are possibly added to the catalytic zone or zones comprising Nickel.

A reactor for the synthesis of urea comprising a vertical shell and perforated baffles or trays (3) arranged to define compartments of the reactor, wherein each baffle comprises an array of individual perforated tiles (10) wherein each tile (101) comprises side walls (101A-101D) and a top face (101F), the side walls having first perforations for the liquid and said top face having second perforations for the gas, wherein said second perforations are smaller than said first perforations, and the tiles are distributed over the baffle with a two-dimensional pattern where adjacent tiles are separated by gaps (17).