Cessna 172 pilot reported safely diverting to an alternate airport after experiencing a loss of engine power.

Narrative

After finishing all necessary preflight and run up checklist on the ground with no abnormalities; I took off from ZZZ. My leaning procedure for the climb and cruise checklist was at 3000ft I leaned to the green arc; and for every 500 ft I turned the mixture one notch to the left (1/6 rotation). When I reached my final cruise altitude of 4;500; I had only turned the knob 1/2 a rotation from my initial lean at 3000ft. I heard the engine drop in power; though I had not adjusted the power. I glanced at my tachometer and noted that my RPM had dropped from 2400 to below 2000 rpm; and stayed there longer than 5 seconds. No engine vibration was noted; and I verified that the mags were on both and fuel shutoff was in. I tried to apply full mixture to see if I had leaned the engine too much and activated the auxilary fuel pump. After not being able to get my power back I informed ZZZ Approach that I wanted to divert into ZZZ1 since it was in my glide distance at the time. I safely landed and was able to taxi to the ramp. ZZZ and ZZZ1 ATC handled the situation promptly and effectively.