Guido Zichittella

Catalyst design for natural-gas upgrading through oxybromination chemistry

Natural gas contains large volumes of light alkanes, and its abundant reserves make it an appealing feedstock for value-added chemicals and fuels. However, selectively activating the C-H bonds in these useful hydrocarbons is one of the greatest challenges in catalysis. Here we report an attractive oxybromination method for the one-step functionalization of methane under mild conditions that integrates gas-phase alkane bromination with heterogeneously catalysed HBr oxidation, a step that is usually executed separately. Catalyst-design strategies to provide optimal synergy between these two processes are discussed. Among many investigated material families, vanadium phosphate (VPO) is identified as the best oxybromination catalyst, as it provides selectivity for CH3Br up to 95% and stable operation for over 100 hours on stream. The outstanding performance of VPO is rationalized by its high activity in HBr oxidation and low propensity for methane and bromomethane oxidation. Data on the oxybromination of ethane and propane over VPO suggest that the reaction network for higher alkanes is more complex.

Selective Production of Carbon Monoxide via Methane Oxychlorination over Vanadyl Pyrophosphate

A catalytic process is demonstrated for the selective conversion of methane into carbon monoxide via oxychlorination chemistry. The process involves addition of HCl to a CH4 -O2 feed to facilitate C-H bond activation under mild conditions, leading to the formation of chloromethanes, CH3 Cl and CH2 Cl2 . The latter are oxidized in situ over the same catalyst, yielding CO and recycling HCl. A material exhibiting chlorine evolution by HCl oxidation, high activity to oxidize chloromethanes into CO, and no ability to oxidize CO, is therefore essential to accomplish this target. Following these design criteria, vanadyl pyrophosphate (VPO) was identified as an outstanding catalyst, exhibiting a CO yield up to approximately 35 % at 96 % selectivity and stable behavior. These findings constitute a basis for the development of a process enabling the on-site valorization of stranded natural-gas reserves using CO as a highly versatile platform molecule.

Olefins from Natural Gas by Oxychlorination

Ethylene and propylene are the key building blocks of the chemical industry, but current processes are unable to close the growing gap between demand and manufacture. Reported herein is an exceptional europium oxychloride (EuOCl) catalyst for the selective (≥95 %) production of light olefins from ethane and propane by oxychlorination chemistry, thus achieving yields of ethylene (90 %) and propylene (40 %) unparalleled by any existing olefin production technology. Moreover, EuOCl is able to process mixtures of methane, ethane, and propane to produce the olefins, thereby reducing separation costs of the alkanes in natural gas. Finally, the EuOCl catalyst was supported on suitable carriers and evaluated in extrudate form, and preserves performance for >150 h under realistic process conditions.

An Activated TiC-SiC Composite for Natural Gas Upgrading via Catalytic Oxyhalogenation

Alkane oxyhalogenation has emerged as an attractive catalytic route for selective natural gas functionalization to important commodity chemicals, such as methyl halides or olefins. However, few systems have been shown to be active and selective in these reactions. Here, we identify a novel and highly efficient TiC–SiC composite for methane and ethane oxyhalogenation. Detailed characterization elucidates the kinetics and mechanism of the selective activation under reaction conditions to yield TiO2–TiC–SiC. This catalyst outperforms bulk TiO2, one of the best reported catalysts, reaching up to 85 % selectivity and up to 3 times higher titanium‐specific space‐time‐yield of methyl halides or ethylene. This is attributed to the fact that the active TiO2 phase generated in situ is embedded in the thermally conductive SiC matrix, facilitating heat dissipation thus improving selectivity control.