你好!Ivan,
They two are almost same. But a little deference:
"抓住“
emphasis : hold and don‘t missing it.
The Structure is: V +O Mostly following by: 抓住机会、抓住机遇
"把握“ emphasis: hold and try your best do it .
The Structure is: V +(complement)+O ,like:把握(好)这次机会、把握(住)这次机会
Hope that's helpful for you ! Thanks~
欢迎大家讨论补充哦~