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We focused on the electronic energy barriers for the first four lowest energy proton - electron transfer steps for reducing CO2 on Pt ( 111 ) beginning with adsorbed * CO2 and continuing with * COOH , * CO + H2O , * COH , and ending with * C + H2O .
 CO2, Pt ( 111 ), CO2, COOH, CO, H2O, COH, C, H2O
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 CO2, Pt ( 111 ), CO2, COOH, CO, H2O, COH, C, H2O