Improving　the　catalytic　selectivity　of　Pd　catalysts　is　of　key　importance　for　various　industrial　processes　and　remains　a　challenge　so　far.　Given　the　unique　properties　of　single-atom　catalysts,　isolating　contiguous　Pd　atoms　into　a　single-Pd　site　with　another　metal　to　form　intermetallic　structures　is　an　effective　way　to　endow　Pd　with　high　catalytic　selectivity　and　to　stabilize　the　single　site　with　the　intermetallic　structures.　Based　on　density　functional　theory　modeling,　we　demonstrate　that　the　(110)　surface　of　Pm　(3)　over　barm　PdIn　with　single-atom　Pd　sites　shows　high　selectivity　for　semihydrogenation　of　acetylene,　whereas　the　(111)　surface　of　P4/mmm　Pd3In　with　Pd　trimer　sites　shows　low　selectivity.　This　idea　has　been　further　validated　by　experimental　results　that　intermetallic　PdIn　nanocrystals　mainly　exposing　the　(110)　surface　exhibit　much　higher　selectivity　for　acetylene　hydrogenation　than　Pd3In　nanocrystals　mainly　exposing　the　(111)　surface　(92%　vs　21%　ethylene　selectivity　at　90　degrees　C).　This　work　provides　insight　for　rational　design　of　bimetallic　metal　catalysts　with　specific　catalytic　properties.