Halogen-mediated alkane functionalization into haloalkanes and olefins and their subsequent conversion into liquid fuels and chemicals constitute an attractive technology with the potential to develop processes for the on-site valorization of natural gas. However, the industrial implementation of this route is contingent on the full recycling of the hydrogen halide (HX, X=Cl, Br), which results from the alkane activation and haloalkanes upgrading steps. Catalytic alkane oxyhalogenation, comprising the reaction of the alkane with HX and O2, allows to integrate alkane functionalization and halogen recovery in a single step. Still, a key challenge to be overcome for the potential application of this route is the availability of efficient catalytic materials as well as the development of advanced characterization techniques as tools enabling the design of active, selective, and stable catalysts. This thesis discovers new families of catalysts and unravels fundamental understanding in the oxychlorination and oxybromination of C1-C4 alkanes, providing guidelines for designing optimal catalytic systems, by combining precise material syntheses, in-depth characterization analyses, detailed kinetic assessments, and advanced spectroscopic techniques. Firstly, methane oxyhalogenation has been investigated over supported metal nanoparticles, revealing activity and selectivity differences as a function of the hydrogen halide. In particular, silica-supported palladium catalysts are identified as the most selective (&98.5%) towards desired halomethanes (CH3X CH2X2) at moderate methane conversion (20%), rivaling the performance of the best oxyhalogenation catalysts reported to date. Kinetic analyses indicate that CH4 oxyhalogenation might proceed via the surface-catalyzed generation of molecular halogen and its reaction with CH4 in the gas phase with free radicals. However, to unravel this mechanism, the detection of these short-lived intermediates under operating conditions is required. This thesis demonstrates operando photoelectron photoion coincidence (PEPICO) spectroscopy as a pivotal method to achieve this goal. In particular, this technique is conducted in methane oxyhalogenation, providing, not only the evidence for the formation of methyl, bromine, and chlorine radicals, but also a strong correlation between methyl halide production and methyl radicals formation. Finally, these findings enable to demonstrate that radical- and surface-based routes are equivalent in oxychlorination, while the observed rate in oxybromination is dominated by gas-phase pathways. In view of the functionalization of higher alkanes, the use of HCl as halogenating agent allows to design catalysts for selective alkane activation as compared to HBr, due to the possibility to confine the reaction to the catalyst surface. In particular, the oxychlorination of ethane and propane is found to selectively (below or equal to 98%) generate ethylene and propylene up to full and high (55%) ethane and propane conversion, respectively, over several catalytic systems, including titanium oxide (TiO2), activated titanium carbide silicon carbide composite (TiO2-TiC-SiC), vanadium phosphate ((VO)2P2O7), and particularly iron phosphate (FePO4), chromium phosphate (CrPO4), and europium oxychloride (EuOCl) in a stable manner for up to 150 h on stream. The comprehensive evaluation of selected benchmark systems in the oxychlorination of ethane, propane, and butane, in combination with in-depth material characterization and kinetic analyses reveals activity and selectivity descriptors as a function of the alkane substrate. In particular, the reactivity of the catalysts is found to correlate with the ability of the material to evolve chlorine, which weakens with increasing carbon number. On the other hand, the olefin selectivity is a function of the rate of dehydrochlorination of the alkyl chloride, which is believed to be the intermediate to the olefin, and of the propensity towards alkane cracking and combustion over the catalysts, both increasing from ethane to butane. Specifically, the ethylene selectivity in ethane oxychlorination is mainly driven by catalytic ethyl chloride dehydrochlorination, while olefin production in propane and especially butane oxychlorination is primarily determined by the tendency of the catalysts to combust and/or crack the alkane, which is found on average moderate for propane and particularly enhanced in the case of butane. Interestingly, the olefin selectivity in the oxybromination of ethane and propane is limited (below or equal to 60% and 30%, respectively) over all investigated systems, due to combustion, cracking, and coking, indicating that the differences in the observed halide-dependent selectivity patterns are catalyst independent and inherent to the oxyhalogenation reaction network. In order to unravel the mechanistic origin of these distinct product distributions, this thesis demonstrates operando PEPICO and prompt-gamma activation analysis (PGAA) as pivotal techniques to unravel mechanisms within complex reaction networks by enabling the detection of short-lived radical species and by quantifying halogen and metal contents over the catalyst surface during operating conditions, respectively. In particular, evidences from these techniques combined with kinetic analyses and detailed material characterization, which were further complemented by density functional theory calculations in the case of ethane oxyhalogenation, demonstrate that while the alkane activation leads to alkyl halide regardless of the halogen source, the major difference lies in where the activation occurs. A chlorinated surface results in the observed selectivity control in oxychlorination whereas the generation of alkyl bromide occurs in the gas phase with the evolved Br2 and Br radicals, promoting undesired side reactions. In addition, operando PEPICO enables the selective detection of propyl radical isomers and provides unprecedented insights into the coking and cracking mechanisms in propane activation via oxybromination, entailing the formation of allyl and propargyl radicals. These findings allowed us to develop a novel catalytic process for the production of ethylene and propylene, which surpasses any existing olefin generation technology, paving the way for the potential implementation of a chlorine-based route for on-site natural gas valorization and giving momentum to future development in the halogen-mediated functionalization of alkanes.