$6.$ Catalytic cracking enhances gasoline yields by using a $\_\_\_\_\_\_\_\_,$ which promotes the breakdown of hydrocarbons at lower $\_\_\_\_\_\_$ and $\_\_\_\_\_\_\_\_.$

$7.$ Hydrocracking combines hydrogen gas with petroleum fractions under high $\_\_\_\_\_\_\_\_,\_\_\_\_\_\_,$ and in the presence of a $\_\_\_\_\_\_\_\_$ to improve yield and quality.

$8.$ Thermal reforming of petroleum improves the $\_\_\_\_\_\_\_\_$ number by changing the $\_\_\_\_\_\_$ structure of the fuel under high $\_\_\_\_\_\_\_\_.$

$9.$ Catalytic reforming uses a $\_\_\_\_\_\_\_\_$ to rearrange the molecular structure of hydrocarbons, enhancing the $\_\_\_\_\_\_$ and $\_\_\_\_\_\_\_\_$ of the resulting fuels.