Catalytic Hydrogenation and stability

[Khyati]

1)Why can the use of high temperatures in the catalytic hydrogenation of alkenes to alkanes be self-defeating ?

2)We know that if the substituent is present at the equatorial position in cyclohexane then that compound is more stable, then why all trans-1,2,3,4,5,6-Hexaisopropylcyclohexane is a stable molecule in which all isopropyl groups are axial ?