import bpy


obj = bpy.context.scene.objects.active # Active Object

mat_names = ["Material.001", "Material", "Material.002"] # names of the materials

mats = []

folder = "C:\test\test" # folder to save the different images in: Remember the double bar (\)!

bf_area_type = bpy.context.area.type

for m in mat_names:

    mats.extend([bpy.data.materials[m]]) #adding the materials based on their names

for i, mat in enumerate(mats):

    #if the object has not material slot, it adds one slot to it.
    if obj.data.materials:

        obj.data.materials[0] = mat
    else:
        obj.data.materials.append(mat)

    #render
    bpy.ops.render.render()

    #change the area type to Image editor
    bpy.context.area.type = "IMAGE_EDITOR"

    #Save the image
    bpy.ops.image.save_as(save_as_render=True, copy=True, filepath=folder+"//Render{}.png".format(i), relative_path=False, show_multiview=False, use_multiview=False)

    #Reset the area type
    bpy.context.area.type = bf_area_type