Recent kinetic simulations of supercritical, quasi-perpendicular shocks yield time varying shock solutions that cyclically reform on the spatio-temporal scales of the incoming protons. Whether a shock solution is stationary or reforming depends upon the plasma parameters which, for SNR shocks are ill defined but believed to be within thetime-dependent regime. We will first review the structure and evolution of the time dependentsolutions, and the acceleration processes of the ions and electrons in these time dependent fields, for a proton-electron plasma. We will then present recent results for a three component plasma: background protons; electrons; and a second heavier ion population. These acceleration mechanisms may generate a suprathermal\"injection$quot; population - a seed population for subsequent acceleration at the shock, which can in turn generate particles at cosmic ray energies.