The down side to the effort to squeeze all the activity out of an existing catalyst is that breakthroughs in catalyst technology are hard won. The hope is that steady increases in catalyst activity combined with improvements in process and reactor technology can close the gap before diesel sulfur regulations go into effect. One leap in catalyst activity was found using ruthenium catalysts, however Ru's high cost outweighs the higher activity. There is some room for improvement in reactor technology and design. For example, concerns about distribution of the oil within catalyst beds have arisen.
Oil is mixed with hydrogen, and the mixture flows onto a tray at the top of the reactor.
The tray attempts to distribute the oil evenly over the top of the catalyst. If it does not, more of the oil flows over one area. This area gets hotter because of the larger amount of oil being reacted exothermically. At higher temperatures, the reactions proceed more quickly, and cracking of the hydrocarbons can occur. This eventually deactivates the area that continues to have higher oil flow through it.