| 423 / | HD | CHEMISTRY OF INORGANIC COMPOUNDS |
| 644 | DF | HYDROGEN OR COMPOUND THEREOF {3} |
| 648.1 | DF | .~ Elemental hydrogen {6} |
| 650 | DF | .~.~ By decomposing hydrocarbon {1} |
| 651 | DF | .~.~.~ Catalytic reaction {1} |
| 652 | | .~.~.~.~ Including decomposing water {1} |
| 653 | DF | .~.~.~.~.~> Catalyst substance contains nickel {1} |