Unable to pxe boot debian9 image

UEFI assumes 64 bits, some vendors do support 32 bits but your mileage can vary. You can try to generate your own grub2 image yourself:

grub2-mkimage -O i386-efi -d /usr/lib/grub/i386-efi -o /var/lib/tftp/grub2/grubia32.efi -p "" all_video boot btrfs cat configfile echo ext2 fat font gfxmenu gfxterm gzio halt hfsplus iso9660 jpeg loadenv loopback lvm mdraid09 mdraid1x minicmd normal part_apple part_msdos part_gpt password_pbkdf2 png reboot search search_fs_uuid search_fs_file search_label serial sleep syslinuxcfg test tftp video xfs linux