Fischer–Tropsch synthesis is a typical reaction for converting synthesis gas (i.e., CO and H2 mixture) to clean fuels, by coupling different processes, which can produce products such as engine fuels and other high value-added chemicals. However, searching for a suitable catalyst is still challenging due to its chemical structure-sensitive properties, which greatly affect the interaction with active components, thereby altering the reaction activity or product selectivity. In this work, the nanosized ZrO2 with different oxygen vacancy concentrations was synthesized by using UiO-66 as a precursor and applied for supporting cobalt nanoparticles. The results showed that treatment of nanosized ZrO2 carrier with diluted nitric acid at an appropriate temperature could effectively modulate its surface oxygen vacancy and subsequently alter the FTS activity. The optimized Co/C-ZrO2-80 catalyst with a high concentration of oxygen vacancy displayed a CO conversion of 44.2% and a cobalt time yield (CoTY) of 20.9 × 10–5 molCO gCo–1 s–1 at 220 °C, which shows a 2.9-fold increase in CoTY compared with the conventional ZrO2-supported catalyst. Multiple characterizations and comparative experiments indicated that oxygen vacancies on the surface of ZrO2 enhanced the electron transfer and the interaction between Zr and Co species. Zr-OV-Co interface sites promoted the adsorption and dissociation of CO and H2 molecules. This work provides a new perspective for studying the effect of oxygen vacancies on the structure and reactivity of cobalt-based FTS catalysts.
The catalytic transformation of renewable fatty acids into value-added fatty alcohols without the use of gaseous hydrogen is a versatile technique for the utilization of microalgae and waste cooking oil, where Cu-based catalysts are considered to be the most suitable candidate. However, the interpretation of the structure–reactivity relationship caused by different crystal types of carriers and the metal–support interface is not well understood. Herein we synthesized ZrO2-supported Cu nanoparticle catalysts via different preparation methods and reduction temperatures under similarly exposed surface facets and Cu valency but different polymorphic phases of ZrO2 (monoclinic ZrO2: m-ZrO2; tetragonal ZrO2: t-ZrO2) and the metal–support interface. Interestingly, the as-synthesized Cu/t-ZrO2 catalysts showed remarkably better catalytic performance than Cu/m-ZrO2 for the in situ hydrogenation of lauric acid in the methanol–water system. Combined experimental and density functional theory (DFT) calculation results ascribed the lower efficiency of m-ZrO2 as a carrier to weakly adsorbed reactant and intermediate molecules as well as the absence of an oxygen vacancy in the crystal phase. The interface-rich Cu/t-ZrO2 catalysts displayed higher activity normalized to the surface-exposed Cu sites toward lauryl alcohol production than the interface-deficient counterparts. DFT calculation results further revealed that this metal–support interface plays an important role in promoting the C–O bond or H–H bond cleavage in two possible reaction routes, thus reducing the activation barrier of the overall reaction.
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