No abstract

In principle, the robust photoreduction of CO 2 relies on catalysts with versatile functions, such as efficient light adsorption, charge separation, and appropriate redox chemistry. [3][4][5] Despite enormous efforts have been dedicated to developing various photocatalysts for CO 2 conversion, most of them suffer from low selectivity and yield of methanol. [6][7][8] Since both CO 2 (CO bonds, ∼750 kJ mol −1 ) and H 2 O (OH bonds, ≈464 kJ mol −1 ) are thermodynamically stable, few catalysts could simultaneously reduce CO 2 and oxidize H 2 O without a hole-scavenger. [9,10] The thermodynamics demands that semiconductor catalysts have a bandgap spanning a wide margin of the reduction and oxidation potentials relevant to the photoreaction. [11] On the contrary, a relatively narrow bandgap has to be compromised to achieve satisfactory solar efficiency. [12][13][14] In this regard, two-dimensional semiconductors (e.g., layered double hydroxides, [15] BiOBr, [16] MoS 2 [17] ) with tunable photochemical properties emerge as the potential promising candidates. The kinetic analysis has reported that CO 2 reduction to CH 3 OH involves a sluggish 6-electrons transferred process, which requires accelerated charge transfer as well as long-lived charge carriers. [18,19] However, the excited electron-hole pairs always tend to recombine. The construction of an internal electric field by surface doping in two-dimensional semiconductors provides an attractive approach to expedite the charge migration and inhibit charge carriers' recombination with spatially separating electrons and holes. [20][21][22] Besides the challenges in tailoring semi-conductive properties, the selectivity of methanol has been limited by complex kinetics of photocatalytic CO 2 reduction, because different products (i.e., CO, CH 4 , and CH 3 OH) share similar thermodynamic potentials. [23] According to the fundamentals learning from electrocatalytic or thermocatalytic CO 2 reduction, [24,25] the preferential formation of CH 3 OH requires appropriate adsorption strength of *CO intermediates on active sites. As yet Cu is the most promising catalyst to produce alcohols owing to their specific d electrons configurations. [26--28] When Cu is present on the photocatalyst, the CO 2 could be promoted the formation of *COOH and *CHO species, which improve CO2 reduction Overall photocatalytic conversion of CO 2 and pure H 2 O driven by solar irradiation into methanol provides a sustainable approach for extraterrestrial synthesis. However, few photocatalysts exhibit efficient production of CH 3 OH. Here, BiOBr nanosheets supporting atomic Cu catalysts for CO 2 reduction are reported. The investigation of charge dynamics demonstrates a strong built-in electric field established by isolated Cu sites as electron traps to facilitate charge transfer and stabilize charge carriers. As result, the catalysts exhibit a substantially high catalytic performance with methanol productivity of 627.66 µmol g catal −1 h −1 and selectivity of ≈90% with an apparent quantum efficiency o...

While molecular sieving is a desirable approach for extracting CO2 from flue gas, water vapor in the flue gas often poses significant difficulty in this separation process. To tackle this challenge, we targeted a squarate-calcium metal–organic framework with strong water stability, Ca­(C4O4)­(H2O), for its pore diameter was in the middle of the kinetic diameters of CO2 and N2. Ca­(C4O4)­(H2O) exhibited excellent separation performance for CO2/N2 (15/85 vol) with adsorption selectivity values of 73 at 1 bar and 298 K. This efficient separation was further confirmed by multicomponent breakthrough experiments. Additionally, Ca­(C4O4)­(H2O) showed strong interaction with CO2 based on the very high isosteric heat of 47.7 kJ/mol. The strong affinity between CO2 and Ca­(C4O4)­(H2O) was further explained with density functional theory calculations, which exhibited that CO2 was bound tightly via hydrogen bonds between the oxygen atoms in CO2 and the hydrogen atoms in H2O, as well as π–π interactions between CO2 and the aromatic ligand in the framework. Furthermore, the cyclic adsorption/regeneration experiments under 100% relative humidity, 15 vol % CO2, and balance N2 demonstrated that Ca­(C4O4)­(H2O) is a promising adsorbent for CO2 removal in practical applications due to its excellent tolerance to water vapor and recyclability.

The pursuit of high metal utilization in heterogeneous catalysis has triggered the burgeoning interest of various atomically dispersed catalysts. Our aim in this review is to assess key recent findings in the synthesis, characterization, structure‐property relationship and computational studies of dual‐atom catalysts (DACs), which cover the full spectrum of applications in thermocatalysis, electrocatalysis and photocatalysis. In particular, combination of qualitative and quantitative characterization with cooperation with DFT insights, synergies and superiorities of DACs compare to counterparts, high‐throughput catalyst exploration and screening with machine‐learning algorithms are highlighted. Undoubtably, it would be wise to expect more fascinating developments in the field of DACs as tunable catalysts.

No abstract