I am sure other learned members of the forum know more, but my suggestion is a RIA Guards, Rifles or Infantry uniform (top/left photo). The low fur hat insignia seems to include separate badges: double-headed eagle, or possibly a multi-rayed star; perhaps a small Romanov cockade; but clearly a scroll/arc with a commemorative inscription/battle honour. This well-known category of insignia should ring a bell, but without photo details, I believe it's no easy task to identify the individual regiment. Perhaps the "Litzen" on his collar lead in a certain direction? Guards?