What do you mean by "conversion". If you mean boiling point converging/cracking it will typically increase continuously as temperature is increased.

If instead you mean removal of a contaminant like S or N at high temperatures there could be an equilibrium limitation that could result in a lower conversion to H2S at higher temperature via mercaptan reversion.

As my research, it's about catalytic hydrogenation of fructose to mannitol. Hydrogen atom would be added into the double bond of fructose structure and then form mannitol. Any research I have studied, it said that conversion of fructose get higher when temperature is high.

It means cracking. When H atom is added, double bond in fructose structure will be cracked and cause mannitol formation.

Hydrogenation reaction involves the saturation of the double bond by addition of hydrogen across the double bond. . The rate of hydrogenation enhances by increase of temperature .

yes, I get it. By the way. The calculation and result for my research said that conversion is decrease when it get higher temp.

How should I discuss this result

Thanakorn Lowasri that is correct. At high temperature the reaction goes to equilibrium and the equilibrium olefin composition increases at higher temperatures

You must take into account two points of view - thermodynamic of hydrogenation reaction and kinetic aspect. Generally, from kinetical point of view, increasing of temperatute increases the rate of all chemical reaction (Arrhenius equation). But from thermodynamic point of view, each hydrogenation reaction is exothermic reaction and the increase of temperature could have negative influence on the equilibrium of composition of saturated - unsaturated compound. So if you reach at lower temperature equilibrium composition of reaction mixture, the increase of temperarure could reflects in the decrease of hydrogenation. It is necessary to know the dependence of equilibrium compositon on temperature.