This type of special consumables (also called XP catalyzer or just cats) help a free to play or unsubscribed player to double the amount of gained experiences. You need to gain at least 100 experinces to take the effect (it does not work with smaller amount) and every hundred of experiences will consume 1 piece of catalyzer. For example, in case your free to play character earns 1450 experiences from an action while catalyzer is activated, the real amount of experiences gained will be 2850 (not 2900) and it will consume 14 pieces of activated catalyzer.
Note: Subscribed characters have permanent catalyzer activated already and do not need to care about it while the subscription is valid.
There exist various qualities of experience catalyzer you can find in the game. Catalyzer do affect only experinces gained with a skill of lower level than the actual catalyzer quality is. This means that a catalyzer of quality 100 will double experiences only for for skills that are at level 99 or lower.
Note: Limit for free to play and unsubscribed characters is at level 125, thus all catalyzer of quality higher than 150 are pointless and can be only used as substitution for quality 150.
There exists several ways how to get experience catalyzer:
All subscribed accounts have permanent catalyzer activated by default and do not have to care about it. Free to play and Unsubscribed characters need to activate them in inventory every time of log into the game or when need to use a new stack of catalyzer. When a catalyzer is activated, you see its icon in the Bonus/Malus window on your screen and the number under this icon says how many pieces left until the catalyser is consumed. Permanent catalyzer of a subscribed character is never consumed and number of pieces remain at 999.
Note: Catalyzer takes effect only on experiences gained with skill of level lower than the catalyzer quality.