Some newer mechanistic aspects investigated by in situ Fourier transform infrared (FTIR) in conjunction with catalytic activity under similar conditions over crystalline lanthanum titanates as a function of Fe substitution at the B-site for the CO + N2O reaction are reported for the first time in the present communication. La2Ti2(1-x)Fe2xO7-delta (0.0 <= x <= 1.0) was synthesized by gel combustion where Fe3+ substitution effectively enhanced the conversion rates for N2O reduction as compared to the pristine La2Ti2O7 (LTOGC). Among all samples, maximum conversion over La2Ti0.8Fe1.2O7-delta [LF(0.6)GC] catalyst was observed. In situ FTIR results reveal that substitution-induced anionic vacancies/defects provide additional sites on the surface of LF(0.6)GC for CO chemisorptions, whereas a perfect stoichiometric lattice like LTOGC is devoid of such sites. Surface-adsorbed CO reacts with surface lattice oxygen in the case of nonstoichiometric LF(0.6)GC to produce carbonates (M-CO32-) at a much lower temperature. The reaction proceeds via carbonate formation, leaving the catalytic surface oxygen deficient in LF(0:6)GC, and therefore facilitates the reduction of preadsorbed, N2O [N2O(g) + *-> N-2 + *-O) by easily adsorbing the oxygen species (*-O) generated in N2O reduction, which is subsequently driven away by adsorbed/gas phase CO, whereas in the case of LTOGC, progress of the reaction was sluggish in the absence of transient carbonate species. Dissociative chemisorptions of N2O are not facilitated on stoichiometric oxygen excess titanate, as there is no vacancy in the surface to accommodate another oxygen atom. The redox mechanism via CO32- species is proposed for CO + N2O reaction over La2Ti2(1-x)Fe2xO7-delta, as against the associative mechanism observed in the unsubstituted sample, La2Ti2O7, as suggested by in situ FTIR in conjunction with catalytic activity results.