CO2 Catalysis Research Articles

Standardization, accreditation, and real-world implementation of photothermal CO2 catalysis

In this activity article, Xiangkun Elvis Cao, impact fellow at MIT Climate & Sustainability Consortium, and Wei Sun, research-stream professor at Zhejiang University, discuss the need for standardization and accreditation to accelerate photothermal CO 2 catalysis research as well as the opportunities and challenges in its real-world implementation. In this activity article, Xiangkun Elvis Cao, impact fellow at MIT Climate & Sustainability Consortium, and Wei Sun, research-stream professor at Zhejiang University, discuss the need for standardization and accreditation to accelerate photothermal CO 2 catalysis research as well as the opportunities and challenges in its real-world implementation.

Photothermal CO2 catalysis: From catalyst discovery to reactor design

In this activity, Wei Sun, research-stream professor at Zhejiang University, and Xiangkun Elvis Cao, impact fellow at MIT Climate & Sustainability Consortium, exchange views on academic and industrial considerations on the two vital elements of the advanced technology for photothermal CO 2 catalysis, i.e., catalyst discovery and reactor design. In this activity, Wei Sun, research-stream professor at Zhejiang University, and Xiangkun Elvis Cao, impact fellow at MIT Climate & Sustainability Consortium, exchange views on academic and industrial considerations on the two vital elements of the advanced technology for photothermal CO 2 catalysis, i.e., catalyst discovery and reactor design.

A simple and versatile synthesis strategy of hollow MOFs for CO2 separation and catalysis.

A novel single-solvent-interfacial strategy is proposed to synthesize hollow MOFs, fabricated at the two-phase interface originated from the self-deliquescence of hydration water in the metallic precursors and the solvents with low water solubility. The as-fabricated HMOFs with hierarchically porous structures exhibit significant enhancement in CO2 separation and catalysis.

Gridlike 3d-4f heterometallic macrocycles for highly efficient conversion of CO2 into cyclic carbonates

Recycle CO2 as a chemical feedstock and as renewable energy generated sustainable solution benefiting both environment and economy. However, advancements in highly efficient CO2 conversion at ambient condition are still hampered, mainly due to the inherent thermodynamic stability of CO2 which lead to the low conversion efficiency and required harsh catalyzing conditions (high temperature, high pressure, and toxic solvents, etc.). In this study, two unique gridlike 3d-4f heterometallic structures Ln8Zn4L6 have been successfully constructed (Ln = Eu(1), Tb(2), H4L = 2,2'-oxybis (N'-((E)-2-hydroxy-3-methoxybenzylidene) acetohydrazide)). The multimetal centers and functional ligand within these Ln8Zn4L6 assembles greatly increased the efficiency of CO2 fixation and promoted the catalysis of CO2 at greener conditions like atmospheric pressure and solvent free. Meanwhile, such heterometallic design showed enhanced stability without being influenced by moisture and impurities. As a proof of concept, these catalysts were further applied in direct catalyzing the simulated flue gas (15 % CO2/85 % N2) in practice and successfully afforded the value-added cyclic carbonate in decent yields. Therefore, the design of such 3d-4f heterometallic macrocycles provided a general and efficient approach for realizing CO2 conversion at greener conditions, which showed great potential in the next generation of CO2 based sustainable chemistry.

Two-dimensional PdMo curved nanosheets for tunable CO2 electrocatalytic reduction to syngas

Summary Syngas (CO/H2) is an essential industrial feedstock. Electroreduction of CO2 to syngas is a desirable solution to energy and environmental challenges. Two-dimensional (2D) nanomaterials have been identified as promising electrocatalysts in CO2 reduction reactions (CO2RRs). Here, we report 2D PdMo curved nanosheets (PdMo CNSs) as the electrocatalyst for efficient, tunable, selective, and stable electroreduction of CO2 to syngas. The H2/CO ratio is tunable from 0.15:1 to 4:1. The current density can be as high as 65.6 mA cm–2 with a H2/CO ratio of 1:1. Density functional theory calculations illustrate that alloying Mo can optimize the electronic structure around Pd and significantly reduce the kinetic energy barrier, thus improving the migration ability of CO∗ and enhancing the anti-poisoning performance of the electrode to achieve more stable CO2 electroreduction. This work offers a strategy for developing new metal-based 2D nanomaterial electrocatalysts for efficient catalysis of CO2 to syngas.

Construction of Fe embedded graphene nanoshell/carbon nanofibers catalyst for catalytic cracking of biomass tar: Effect of CO2 etching

Carbon-based metal catalyst has attracted wide attention in the utilization for tar catalytic cracking because of its high hierarchical porous structure and high dispersion of metal particles. In this study, sawdust was used as raw material to prepare Fe embedded graphene nanoshell/carbon nanofibers catalyst for catalytic cracking of biomass tar by impregnation followed by carbothermal reduction in CO2 atmosphere. The properties of the catalysts were evaluated by a variety of characterization methods and based on which the evolutionary mechanism was proposed. CO2 etching improved the porosity (Vtotal = 0.4187 cm3/g and BET surface area = 225.93 m2/g) and increased the content of Fe0. During CO2 etching and catalysis of FeCl3, the prepared catalyst formed a structure in which a large amount of carbon nanofibers/graphene shells wrapped metallic iron deposited on the porous carbon support. The stacking of carbon nanofibers enhanced the adsorption capacity of the catalyst to tar macromolecules. The coating of the graphene shell to the metal nanoparticles prevented the agglomeration and sintering of metal active sites, which increased the stability of the catalyst. The results indicated that the Fe@C800C1 catalyst showed good catalytic performance at 700 °C, and the tar conversion efficiency reached up to 90.4%. After 4 cycles, the tar removal efficiency still maintained at 90.0%.

Mechanistic Connections between CO2 and CO Hydrogenation on Dispersed Ruthenium Nanoparticles.

Catalytic routes for upgrading CO2 to CO and hydrocarbons have been studied for decades, and yet the mechanistic details and structure-function relationships that control catalytic performance have remained unresolved. This study elucidates the elementary steps that mediate these reactions and examines them within the context of the established mechanism for CO hydrogenation to resolve the persistent discrepancies and to demonstrate inextricable links between CO2 and CO hydrogenation on dispersed Ru nanoparticles (6-12 nm mean diameter, 573 K). The formation of CH4 from both CO2-H2 and CO-H2 reactants requires the cleavage of strong C≡O bonds in chemisorbed CO, formed as an intermediate in both reactions, via hydrogen-assisted activation pathways. The C═O bonds in CO2 are cleaved via direct interactions with exposed Ru atoms in elementary steps that are shown to be facile by fast isotopic scrambling of C16O2-C18O2-H2 mixtures. Such CO2 activation steps form bound CO molecules and O atoms; the latter are removed via H-addition steps to form H2O. The kinetic hurdles in forming CH4 from CO2 do not reflect the inertness of C═O bonds in CO2 but instead reflect the intermediate formation of CO molecules, which contain stronger C≡O bonds than CO2 and are present at near-saturation coverages during CO2 and CO hydrogenation catalysis. The conclusions presented herein are informed by a combination of spectroscopic, isotopic, and kinetic measurements coupled with the use of analysis methods that account for strong rate inhibition by chemisorbed CO. Such methods enable the assessment of intrinsic reaction rates and are essential to accurately determine the effects of nanoparticle structure and composition on reactivity and selectivity for CO2-H2 reactions.

Comparative study of CO2 activation on alkali metals encapsulated III–V hollow nanocages: An insight from first-principles calculations

Density functional theory calculations have been applied to explore a series of 12 selected nano-hollow cages A12X12 for catalysis of CO2 to hydrogenated products. The reactivity order among the nanocages is found to be A12N>12A12P>12A12As12. Among the 12 selected nano-hollow cages, only six nanocages are able to activate CO2 molecule. Surprisingly, endohedral doping of alkali metals (Li, Na, K) leads to a decrease in band gap, increases charge separation and hereby increases the adsorption energies. Additionally, while the undoped A12As12 nanocages remain inert for CO2 activation alkali metal doped A12As12 nanocages showed an increased level of CO2 activation. Furthermore, among the alkali metals, potassium doped endohedral nanocages showed increased adsorption energy and the least energy barrier for CO2 activation. These findings have immense importance to provide new ideas for the design of potential nanocages catalyst for CO2 reduction.

Investigation into the Re-Arrangement of Copper Foams Pre- and Post-CO2 Electrocatalysis

The utilization of carbon dioxide is a major incentive for the growing field of carbon capture. Carbon dioxide could be an abundant building block to generate higher-value chemical products. Herein, we fabricated a porous copper electrode capable of catalyzing the reduction of carbon dioxide into higher-value products, such as ethylene, ethanol and propanol. We investigated the formation of the foams under different conditions, not only analyzing their morphological and crystal structure, but also documenting their performance as a catalyst. In particular, we studied the response of the foams to CO2 electrolysis, including the effect of urea as a potential additive to enhance CO2 catalysis. Before electrolysis, the pristine and urea-modified foam copper electrodes consisted of a mixture of cuboctahedra and dendrites. After 35 min of electrolysis, the cuboctahedra and dendrites underwent structural rearrangement affecting catalysis performance. We found that alterations in the morphology, crystallinity and surface composition of the catalyst were conducive to the deactivation of the copper foams.

Steam-promoted Methane-CO2 reforming by NiPdCeOx@SiO2 nanoparticle clusters for syngas production

We demonstrate a facile aerosol-based approach to fabricate hybrid nanostrcutures, NiPdOx-CeO2 nanoparticles deposited on the SiO2 nanoparticle clusters, for the catalysis of steam-promoted CO2 reforming with methane. Ultrafine crystallites of active metal and promoter (≈5 nm) are created with tunable cluster sizes and chemical compositions. A superior catalytic performance achieves at low temperature (550 °C): remarkable turnover frequency (≈2 s−1), tunable H2/CO ratio (1.1–1.9) and high 100-h operation stability. Incorporation of SiO2 nanoparticle cluster as support material increases dispersion of active metals and suppresses metal sintering during material synthesis and catalysis. Hybridization with Pd significantly improves the activity of Ni-based catalyst especially ≤600 °C. Addition of steam suppresses the coke formation by > 10 times. The work demonstrates a prototype study of developing bimetallic hybrid nanocatalysts homogeneously dispersed with promoter on the NPC mesoporous support by design, showing promise for the syngas production via synergistic catalysis of methane-CO2 reforming.

A non-equilibrium atmospheric pressure Capacitively-Coupled-Plasma (CCP) driven at VHF (162 MHz) for plasma catalysis of CO2 into CO

The design of a Very-High-Frequency (VHF) 162 MHz driven atmospheric-pressure Capacitively-Coupled-Plasma (CCP), with top and bottom electrodes operated in push-pull configuration, powered via a Power-Splitting-Transmission-Line-Driver (PSTLD), is presented. Application to the reprocessing of carbon dioxide into carbon-monoxide in this "high” VHF atmospheric plasma is presented, demonstrating some behaviour of the plasma source. rf power in the system is characterized using measured current (~ 1′s Amps peak) and voltage (~ 10′s Volts peak) waveforms at the electrode; Both are sinusoidal confirming a glow-discharge operational condition. Analysis of Optical Emission Spectra results find a highly non-equilibrium plasma, with high vibrational temperatures (from N2) in the range ~4000 K, while gas temperature, monitored by a thermocouple at the gas outlet, remains low ~300 K, and confirmed by analysis of the N2 rotational bands. The relative density of CO produced, as a by-product of CO2 dissociation, is measured optically using N2 as an actinometer. The CO density increases with rf power and longer gas residence times in the plasma volume. The high VHF atmospheric plasma is found to operate in pure CO2 flows (no helium) with minimal gas heating for the full range of power densities (specific energy input of 0.4–2 eV per molecule) investigated.

Copper‐Based Metal‐Organic Framework for Selective CO2 Adsoprtion and Catalysis Fixation of CO2 into Cyclic Carbonates

AbstractGiven the capture and utilization of carbon dioxide (CO2) emission, the CO2 separation and catalysis fixation of CO2 and epoxides have been of intense interest. In this respect, a microporous copper‐based metal‐organic framework (MOF) Cu2(ABTC) (ABTC=3,3’,5,5’‐azobenzenetetra‐carboxylic acid) was synthesized. The Cu–MOF endowed with open Cu sites, accessible pore cages and hexagonal channel (9.6 & 11 Å) exhibits permanent porosity (BET surface area of 2200 m2 g−1), good low‐pressure CO2 uptake (93 cm3 g−1, at 298 K), and moderate CO2 selectivity over N2 and CH4. In light of catalysis fixation of CO2 and epoxides, Cu2(ABTC) exhibited outstanding performance with high conversion of styrene oxide (96 %), and yield towards the formation of styrene carbonate (90 %) under mild conditions (1 atm of CO2, 60 °C, 8 h). Notably, the catalytic activity of Cu2(ABTC) outperformed that of other Cu‐MOFs, and the recovered Cu2(ABTC) can be reused up to six times without considerable reduction in catalytic activity.

A core-shell catalyst design boosts the performance of photothermal reverse water gas shift catalysis

Photothermal reverse water gas shift (RWGS) catalysis holds promise for efficient conversions of greenhouse gas CO2 and renewable H2, powered solely by sunlight, into CO, an important feedstock for the chemical industry. However, the performance of photothermal RWGS catalysis over existing supported catalysts is limited by the balance between the catalyst loading and dispersity, as well as stability against sintering. Herein, we report a core-shell strategy for the design of photothermal catalysts, by using Ni12P5 as an example, with simultaneously strong light absorption ability, high dispersity and stability. The core-shell structured Ni12P5@SiO2 catalyst with a relatively small Ni12P5 particle size of 15 nm at a high Ni12P5 loading of 30 wt% exhibits improved activity, nearly 100% CO selectivity, and superior stability in photothermal RWGS catalysis, particularly under intense illuminations. Our study clearly reveals the effectiveness of the core-shell strategy in breaking the limitation of supported catalysts and boosting the performance of photothermal CO2 catalysis.

Niobium and Titanium Carbides (MXenes) as Superior Photothermal Supports for CO2 Photocatalysis.

The conversion of CO2 into fuels and feedstock chemicals via photothermal catalysis holds promise for efficient solar energy utilization to tackle the global energy shortage and climate change. Despite recent advances, it is of emerging interest to explore promising materials with excellent photothermal properties to boost the performance of photothermal CO2 catalysis. Here, we report the discovery of MXene materials as superior photothermal supports for metal nanoparticles. As a proof-of-concept study, we demonstrate that Nb2C and Ti3C2, two typical MXene materials, can enhance the photothermal effect and thus boost the photothermal catalytic activity of Ni nanoparticles. A record CO2 conversion rate of 8.50 mol·gNi-1·h-1 is achieved for Nb2C-nanosheet-supported Ni nanoparticles under intense illumination. Our study bridges the gap between photothermal MXene materials and photothermal CO2 catalysis toward more efficient solar-to-chemical energy conversions and stimulates the interest in MXene-supported metal nanoparticles for other heterogeneous catalytic reactions, particularly driven by sunlight.

Solar Photocatalysis

Solar Photocatalysis

Amino acid ionic liquids as efficient catalysts for CO2 capture and chemical conversion with epoxides under metal/halogen/cocatalyst/solvent-free conditions

Biocompatible amino acid ionic liquids (AAILs) were synthesized and efficiently applied in CO2 capture and catalysis for the coupling reaction of CO2 with epoxides under halogen-, cocatalyst- and organic solvent-free conditions.

Cell size influences inorganic carbon acquisition in artificially selected phytoplankton.

Cell size influences the rate at which phytoplankton assimilate dissolved inorganic carbon (DIC), but it is unclear whether volume-specific carbon uptake should be greater in smaller or larger cells. On the one hand, Fick's Law predicts smaller cells to have a superior diffusive CO2 supply. On the other, larger cells may have greater scope to invest metabolic energy to upregulate active transport per unit area through CO2 -concentrating mechanisms (CCMs). Previous studies have focused on among-species comparisons, which complicates disentangling the role of cell size from other covarying traits. In this study, we investigated the DIC assimilation of the green alga Dunaliella tertiolecta after using artificial selection to evolve a 9.3-fold difference in cell volume. We compared CO2 affinity, external carbonic anhydrase (CAext ), isotopic signatures (δ13 C) and growth among size-selected lineages. Evolving cells to larger sizes led to an upregulation of CCMs that improved the DIC uptake of this species, with higher CO2 affinity, higher CAext and higher δ13 C. Larger cells also achieved faster growth and higher maximum biovolume densities. We showed that evolutionary shifts in cell size can alter the efficiency of DIC uptake systems to influence the fitness of a phytoplankton species.

Sustainable synthesis of multifunctional porous metalloporphyrin polymers for efficient carbon dioxide transformation under mild conditions

Multifunctionalization of porous organic polymers (POPs) for working in concert on a substrate is now a research topic in CO2 catalysis, yet it remains challenging. This work describes a pre- and post-synthetic strategy to design metalloporphyrin-based azo-hierarchical porous ionic polymers (ZnTPP/QA-azo-PiPs), which were synthesized based on diazo-coupling reaction of tetra(4-aminophenyl) porphyrin zinc with tri/diphenols in aqueous solution under mild conditions, followed by etherification with quaternary ammonium bromide. This synthetic approach endows ZnTPP/QA-azo-PiP1 with features of an improved surface area (181 m2/g), hierarchical porosity, and high-density active sites. ZnTPP/QA-azo-PiP1 presented a noteworthy CO2 uptake of 1.77 mmol/g at 273 K and 1.0 bar and good CO2/N2 selectivity of 44.8. As expected, ZnTPP/QA-azo-PiP1 showed quantitative conversion and selectivity for a range of epoxides under mild conditions (1.0 MPa, 80 °C, 12 h) in the CO2 cycloaddition reaction. ZnTPP/QA-azo-PiP1 could been recycled easily and retained complete retention of activity and selectivity for over 7 cycles. Moreover, with efficacious activity in conversion of diluted CO2 (15% CO2 in 85% N2, v/v), ZnTPP/QA-azo-PiP1 could smoothly catalyze CO2-involved reaction to produce oxazolidinones and N-formylated amines under mild conditions. This work promotes sustainable synthesis of advanced multifunctional POPs and gives great promise for their application in synthetic transformations of CO2.

NHC-stabilized Al(III) and Ga(III) cationic alkyls: Synthesis, structure and use in hydrosilylation catalysis

Cationic Al(III) and Ga(III) species supported by N-heterocyclic carbene (NHC) ligands, (IDipp)AlMe2(PhBr)]+ ([1]+, IDipp = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) and (IDipp)GaMe2]+ ([2]+), were prepared and structurally characterized as B(C6F5)4− salts via ionization of the corresponding neutral precursors (IDipp)MMe3 (M = Al, Ga) with [Ph3C][B(C6F5)4] in PhBr at room temperature. Both [1][B(C6F5)4] and [2][B(C6F5)4] salt were isolated in high yield and their solid state structures established through X-ray crystallographic studies. Cations [1]+ and [2]+, which are rare examples of structurally characterized tris-organyl Al(III) and Ga(III) cations, stand as potent Lewis acids as experimentally estimated through the Gutmann-Beckett method. These cations were further exploited in hydrosilylation catalysis of alkynes, benzaldehyde and CO2 using HSiEt3 as an hydrosilane source. Hydrosilylation of 1-hexyne, 4-phenylbutyne and phenylacetylene led to the formation of the corresponding Z-selective products 3–5, respectively, while benzaldehyde was converted to PhCH2OSiEt3 (6). Cations [1]+ and [2]+ also slowly catalyze CO2 hydrosilylation with the selective formation of the methanol-equivalent MeOSiEt3.

Emerging material engineering strategies for amplifying photothermal heterogeneous CO2 catalysis

A fundamental understanding of basic driving forces and the role of light in photothermal CO 2 catalysis is covered. The progress of the catalyst development and corresponding material engineering strategies are summarized. Closing the carbon loop, through CO 2 capture and utilization, is a promising route to mitigate climate change. Solar energy is a sustainable energy source which can be exploited to drive catalytic reactions for utilizing CO 2 , including converting the CO 2 into useful products. Solar energy can be harnessed through a range of different pathways to valorize CO 2 . Whilst using solar energy to drive CO 2 reduction has vast potential to promote catalytic CO 2 conversions, the progress is limited due to the lack of understanding of property-performance relations as well as feasible material engineering approaches. Herein, we outline the various driving forces involved in photothermal CO 2 catalysis. The heat from solar energy can be utilized to induce CO 2 catalytic reduction reactions via the photothermal effect. Further, solar energy can act to modify reaction pathways through light-matter interactions. Light-induced chemical functions have demonstrated the ability to regulate intermediary reaction steps, and thus control the reaction selectivity. Photothermal catalyst structures and specific catalyst design strategies are discussed in this context. This review provides a comprehensive understanding of the heat-light synergy and guidance for rational photothermal catalyst design for CO 2 utilization.