We don't know much about early evolution of life. However it is believed that energetic molecules (analogous to ATP) may have evolved before everything else. These energetic molecules may have driven different metabolic reactions (which need not be catalyzed by big protein enzymes). Also, it is believed that natural chemical gradients would have been used by primitive life-forms to obtain the energy.
You can have a look at this article. I am pasting the list of references/recommended reading mention in this article so that you may search for them individually even if this article is not accessible any longer.
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