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In this work, following Part 1 that has found a redispersion process from Pt nanoparticles (NPs, about 3.4 nm) to nanoclusters (NCs, about 1 nm) on TiO2and elucidated its mechanism, we carefully investigated the catalytic performance of the obtained Pt NC catalyst in CO oxidation as well as the corresponding reaction mechanism. The Pt NC catalyst excels than its parent catalyst in terms of both intrinsic and apparent activity. Detailed studies by combining kinetic measurements, isotopic labeling reaction experiments, and low-temperature operando FT-IR unambiguously demonstrated that the Pt NCs deposited on TiO2can form unique interfacial sites that enable to active O2at very low temperature, thus the CO adsorbed on TiO2can diffuses to, and reacts with, the activated oxygen, rendering a high activity at low temperatures. This work is contributory in understanding the origin of the high activity of the supported metal cluster catalysts.

Supported metal nanoclusters (NCs) are regarded as the next generation of catalyst that bridge the nanocatalyst and single-atom catalyst. However, feasible fabrication of thermally stable NCs has remained a daunting challenge. In this paper, the first part of an extended work, we report a simple route to fabricate Pt NCs in size of around 1 nm through redispersion of Pt nanoparticles (NPs) or commercial PtO2by a calcination treatment. Combining control experiments and detailed DFT simulation, the whole redispersion process was described and evidenced to proceed via a gas-phase trapping way: Under promotion of oxygen atmosphere and high temperature, volatile oxidized Pt monomers were firstly generated and then trapped by surface defects, forming special sites that preferentially induce the growth of clusters on them. The growing clusters have both size- and temperature-dependent stability, resulting a most stable size distribution of around 1 nm when fabricated at 550 °C. This work provides a feasible top-down strategy to fabricate highly dispersed metal clusters.

In this work, manganese well-dispersed on Fe3O4microsphere (Mn–Fe3O4) catalyst was synthesized. It exhibited excellent catalytic performance for the direct conversion of carbon dioxide (CO2) into light olefins. A CO2conversion of 44.7% with high selectivity of light olefin (46.2%, yield of 18.7%), high O/P ratio (6.5), and low selectivity of CO (9.4%) was obtained over the 10Mn–Fe3O4catalyst. The Mn–Fe3O4catalyst was studied by XRD, SEM, (HR)TEM, STEM–EDS, H2-TPR, and CO2-TPD. The result indicated that the manganese promoter could facilitate the adsorption of CO2and the activation of C═O bonds as well as inhibit the secondary hydrogenation. This work offered a novel Fe-based catalyst system to the utilization of CO2and an understanding in promoting C═O bond activation in the first step of CO2hydrogenation to hydrocarbon reaction.

Optimization of zeolite geometries to break through the current selectivity limitations of CO2hydrogenation for the synthesis of high-value paraxylene (PX) is a promising and challenging topic. Herein, twinned HZSM-5 (LZ5) with a high sinusoidal pore opening ratio was synthesized, and the tandem catalyst formed by coupling it with an iron-based catalyst could realize the highly selective production of PX by CO2hydrogenation. Under industrially relevant conditions, the CO2conversion was 31.5%, and the selectivies for PX in aromatics and in xylene (X) were as high as 34.0 and 90.0%, respectively. This good performance was attributed to the high sinusoidal pore opening ratio of the LZ5 in the tandem catalyst, improving its ability to screen xylene isomers. The particle size of LZ5 has a small effect on the selectivity of CO2hydrogenation to PX. In addition, the proper proximity of the two components also played a crucial role in the continuous and cocatalytic conversion of CO2to PX. The present work realized the improvement in the selective catalytic performance of zeolites through directional modulation of their pore structures and provided a new idea for the design of efficient catalysts in the hydrogenation of CO2to PX.

Direct CO2hydrogenation to value-added chemicals not only decreases carbon emissions but also provides an alternative way for fossil fuels. Even though some outstanding results were obtained, the high productivity of the target product is still hard to achieve. In this work, we fabricated a bifunctional catalyst comprising a Cu-modified Fe-based catalyst and ZSM-5 for selective CO2hydrogenation to aromatics with the help of XRD, H2-TPR, CO2-TPD, SEM, TEM and N2adsorption and desorption techniques for the catalytic mechanism of the prepared catalysts. The results show that the Cu promoter can improve the carbon-chain growth, suppress methane formation over the Fe-based catalyst, and then increase the aromatic selectivity over the bifunctional catalyst, suggesting that heavy olefin-based intermediates are more prone to aromatization than light intermediates. By lengthening the straight channel length of zeolites in the direction of the b-axis, a STYtolueneof 14.8 gCH2·kgcat–1·h–1is obtained. The relevant mechanism may be attributed to the increase in the b-axis length, which restricts the diffusion of products on the straight channel, forcing the product to diffuse from the sinusoidal channel in the ZSM-5 zeolite. This work provides insights for designing a bifunctional catalyst that achieves high productivity of high value-added aromatics.