The reformer is composed of a large number of tubes filled with a catalyst (usually nickel-based) which is used to promote the reaction. Natural gas passes through the catalyst filled tubes to produce H₂, CO and CO₂. The reaction takes place on a thin area around the surface of the catalyst modules. Thus, by adjusting the shape of the catalyst so that the Geometric Surface Area per unit volume (GSA) is increased, the catalyst activity can be improved. Also, by adjusting the shape of the catalyst modules, the Heat Transfer Coefficient (HTC) can increase due to improved catalyst packaging and better contact with the tube walls. The use of improved catalyst designs with increased module voidage and/or size will also lower the pressure drop (PD) (Beyer et al., 2005 p.4). In recent years, complex designs aiming at increasing the pellet voidage or the module surface are using multiple holes and flutes to the outer surface (see image below). 

By improving the shape and the size of the catalyst, the tube side heat coefficients for a target pressure drop can be improved by 20-40% (Malhotra and Knez, 2002). A combination of more than one catalyst sizes can also be used, with the larger modules being used in the lower part of the tubes where  the biggest part of pressure drops take place (Topsoe, unknown date). The main benefits from using improved catalyst designs are improved throughput and lower pressure drops.