Selective oxidation of hydrocarbons into synthesis gas at short contact times: Design of monolith catalysts and main process parameters

摘要

This review summarizes the main achievements of the Boreskov Institute of Catalysis (Siberian Division, Russian Academy of Sciences) in the development of efficient and stable monolith catalysts for selective oxidation of hydrocarbons into synthesis gas at short contact times. Research in this field has included (1) design of new types of active component based on metal oxides, (2) design of new types of monolith support and development of supporting procedures for active components, and (3) optimization of process parameters for different types of fuel (natural gas, isooctane, and gasoline) and oxidant (air oxygen, including its mixtures with water and carbon dioxide), including the start-up regime. Design of active components (platinum, nickel, or their combination) supported on fluorite-like solid solutions based on cerium dioxide and rare-earth (samarium, gadolinium, and praseodymium) or zirconium cations has been aimed at separating hydrocarbon activation (on metal sites) and oxidation (on the support) and conjugating the separated steps of hydrocarbon oxidation at the metal-oxide interface. Optimization of oxygen mobility in the support lattice by varying the nature and concentration of doping cation along with optimization of hydrocarbon activation on supported metal clusters allow hydrocarbons to be completely converted into synthesis gas by selective oxidation or dry or steam reforming at contact times of a few milliseconds, ruling out undesirable carbon build-up on the catalyst surface. The development of new types of monolith support has targeted the enhancement of thermal shock resistance, including testing of supports based on thermally stable metal foils and composites (cermets). The main steps of the production of these supports have been refined, including unique technologies of blast dusting and hydrothermal treatment. The electric conductivity of these systems allows a quick startup of selective oxidation to be performed by passing electric current, and their thermal conductivity minimizes the temperature gradient arising from heat transfer in the bed. Procedures for loading monolith supports with active components have been developed, including impregnation, washcoating, or encapsulation in cermet matrices. The catalysts produced show a high efficiency and an operational stability adequate to the above tasks in the selective oxidation and steam-air autothermal reforming of natural gas (including processes under pressure), isooctane, and gasoline into synthesis gas.