A catalyst system includes a complex having formula I which advantageously has a sterically protecting N-heterocyclic carbene (NHC) carbene-pyridine ligand to handle harsh reactions conditions than many prior art catalysts: wherein M is a transition metal; o is 0, 1, 2, 3, or 4; R1 is a C1-6 alkyl, a C6-18 aryl, or an optionally substituted C5-18 heteroaryl. In a refinement, R1 is methyl, ethyl, butyl, n-propyl, isopropyl, n-butyl, sec-butyl, or t-butyl; R2, R3, R3′ are independently an optionally substituted C1-6 alkyl, halo (e.g., Cl, F, Br, etc), NO2, an optionally substituted C6-18 aryl, or an optionally substituted C5-18 heteroaryl; R4, R4′ are independently an optionally substituted C1-6 alkyl, halo, NO2, an optionally substituted C6-18 aryl, or an optionally substituted C5-18 heteroaryl; and X− is a negatively charge counter ion and L1, L2 are each independently a neutral ligand.