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The emission controls of carbon oxides (CO x) are crucial to fulfill carbon neutrality, where CO x is a useful building block for chemical synthesis. Therefore, CO x conversions have been intensively investigated to reduce carbon emissions and to produce alternative fuels such as dimethyl ether, C 5+ higher hydrocarbons, and higher alcohols by using heterogeneous catalysts. There are lots of advantages in catalytic conversion strategies, which can be largely affected by reaction conditions and types of catalysts. In the paper, catalytic activities and reaction mechanisms of CO x conversions are briefly summarized to elucidate recent progresses of various catalytic reactions. Furthermore, the strategies to improve catalytic activity and stability as well as adjustments of final products selectivity are summarized. Various tandem reactions with well-designed hybridized catalysts to efficiently utilize CO/CO 2 containing syngas are summarized to explain recent synthetic strategies for the productions of value-added hydrocarbon fuels and oxygenates by using environmentally benign catalytic processes. [Display omitted] • CO x conversions to value-added hydrocarbons fuels and oxygenates are reviewed. • Selective hydrogenations of COx by various tandem reactions are summarized. • Well-designed hybridized catalysts with their preparation strategies are reviewed. [ABSTRACT FROM AUTHOR]

• Seed-derived ferrierite (FER) without any organic structure-directing agent (OSDA) showed a higher activity and stability. • Optimal amount of commercial FER-seed (15 wt%FER) stabilized Brønsted acidic sites. • Less formation of coke precursors was obserbed by decreasing Lewis acidic EFAL defect sites. The seed-derived ferrierite zeolite (FER) synthesized at different contents of FER seed component without using any organic structure-directing agent (OSDA) showed a higher catalytic activity and stability for a gas-phase carbonylation of dimethyl ether (DME) to methyl acetate (MA) at an optimal amount of the previously synthesized FER-seed with 15wt%. The optimal amount of FER-seed material played an important role to optimize the numbers of active Brønsted acid sites in 8-membered ring (8-MR) channels with less formation of coke precursors by decreasing defect sites through their recrystallization during the preparation step. The defected Lewis acidic extra-framework aluminum (EFAL) sites on the seed-derived FER surfaces were responsible for preferential coke depositions and for a retarded CO insertion by decreasing the rate of the gas-phase DME carbonylation reaction. [ABSTRACT FROM AUTHOR]

An indirect ethanol synthesis in terms of carbon neutral strategy by consuming synthesis gas consists of three separate steps such as syngas to dimethyl ether (DME), DME carbonylation and methyl acetate (MA) hydrogenation through tandem reactions. For the series reactions, the nanosheet ferrierite (FER) zeolite was used for a gas-phase DME carbonylation reaction to MA and the Cu-ZnO-Al 2 O 3 (CZA)-based catalyst was modified with additional metal oxide promoter (M = Ga, In and Nd) for MA hydrogenation, where the CZA-M catalysts were prepared by a simple coprecipitation method. The CZA-M catalysts hybridized with FER zeolite showed different catalytic activity for the tandem reactions, where the catalytic activity was largely affected by the CZA-M surface properties. The effects of additional metal oxides promoter on the CZA-M were carefully investigated and the CZA-Nd catalyst having larger Cu crystallites showed the best catalytic activity due to the enhanced oxygen vacant sites correspond to their basic sites. [Display omitted] • Direct ethanol synthesis was verified by successive carbonylation and hydrogenation. • FER zeolite hybridized with Cu-ZnO-Al 2 O 3 -Nd revealed a higher ethanol yield. • Larger Cu+ sites and Bronsted acid sites were to enhance catalytic activity and stability. [ABSTRACT FROM AUTHOR]

Dimethyl ether (DME) can be directly synthesized by carbon dioxide (CO 2) hydrogenation over bifunctional catalysts, which are suffered from various deactivation mechanisms caused by incompatible integrations of metal oxides and solid acid zeolites according to their different proximity. The core-shell structured integrations of Cu-ZnO-Al 2 O 3 metal oxide (CZA) and ferrierite zeolite (FER) are investigated for direct CO 2 hydrogenation to DME. The detrimental and undesired surface properties formed by a possible ion-exchange of FER surfaces with the relatively volatile metal ions from Cu-ZnO-Al 2 O 3 surfaces were effectively suppressed by applying the physically-coated interlayers with SiO 2 (CZA@FER) compared to the powder-mixed one (CZA/FER), where an intimate proximity of metal oxides and FER was eventually responsible for an increased CO selectivity and deactivation rate. The SiO 2 interlayers to isolate the CZA and FER with a suppressed migration of metal ions to FER surfaces further stabilized the active Cu-ZnO nanoparticles and acidic sites of FER surfaces. [Display omitted] • Deactivation was from incompatible natures of metal oxides/zeolite with different proximity. • SiO 2 interlayers isolated Cu-ZnO-Al 2 O 3 and FER component with small metal migrations. • FER zeolite surfaces were stabilized by enhancing the compatibility of two stable active sites. [ABSTRACT FROM AUTHOR]