Conversion of carbon dioxide to valuable petrochemicals:An approach to clean development mechanism

The increase of atmospheric carbon dioxide and the global warming due to its greenhouse effect resulted in worldwide concerns. On the other hand, carbon dioxide might be considered as a valuable and renewable carbon source. One approach to reduce carbon dioxide emissions could be its capture and recycle via transformation into chemicals using the technologies in C1 chemistry. Despite its great interest, there are difficulties in CO2 separation on the one hand, and thermodynamic stability of carbon dioxide molecule rendering its chemical activity low on the other hand. Carbon dioxide has been already used in petrochemical industries for production of limited chemicals such as urea. The utilization of carbon dioxide does not necessarily involve development of new processes, and in certain processes such as methanol synthesis and methane steam reforming, addition of CO2 into the feed results in its utilization and increases carbon efficiency. In other cases, modifications in catalyst and/or processes, or even new catalysts and processes, are necessary. In either case, catalysis plays a crucial role in carbon dioxide conversion and effective catalysts are required for commercial realization of the related processes. Technologies for CO2 utilization are emerging after many years of research and development efforts.

Metal-organic frameworks MOF-808-X as highly efficient catalysts for direct synthesis of dimethyl carbonate from CO_2 and methanol

A series of metal-organic frameworks MOF-808-X(6-connected)were synthesized by regulating the ZrOCl2·8H2O/1,3,5-benzenetricarboxylic acid(BTC)molar ratio(X)and tested for the direct synthesis of dimethyl carbonate(DMC)from CO2 and CH3OH with 1,1,1-trimethoxymethane(TMM)as a dehydrating agent.The effect of the ZrOCl2·8H2O/BTC molar ratio on the physicochemical properties and catalytic performance of MOF-808-X was investigated.Results showed that a proper ZrOCl2·8H2O/BTC molar ratio during MOF-808-X synthesis was fairly important to reduce the redundant BTC or zirconium clusters trapped in the micropores of MOF-808-X.MOF-808-4,with almost no redundant BTC or zirconium clusters trapped in the micropores,exhibited the largest surface area,micropore size,and the number of acidic-basic sites,and consequently showed the best activity among all MOF-808-X,with the highest DMC yield of 21.5% under the optimal reaction conditions.Moreover,benefiting from the larger micropore size,MOF-808-4 outperformed our previously reported UiO-66-24(12-connected),which had even more acidic-basic sites and larger surface area than MOF-808-4,mainly because the larger micropore size of MOF-808-4 provided higher accessibility for the reactant to the active sites located in the micropores.Furthermore,a possible reaction mechanism over MOF-808-4 was proposed based on the in situ FT-IR results.The effects of different reaction parameters on DMC formation and the reusability of MOF-808-X were also studied.

CO_(2)electrolysis:Advances and challenges in electrocatalyst engineering and reactor design

Electrochemical reduction of CO_(2)(CO_(2)RR)coupled with renewable electrical energy is an attractive way of upgrading CO_(2)to value-added chemicals and closing the carbon cycle.However,CO_(2)RR electrocatalysts still suffer from high overpotential,and the complex reaction pathways of CO_(2)RR often lead to mixed products.Early research focuses on tuning the binding of reaction intermediates on electrocatalysts,and recent efforts have revealed that the design of electrolysis reactors is equally important for efficient and selective CO_(2)RR.In this review,we present an overview of recent advances and challenges toward achieving high activity and high selectivity in CO_(2)RR at ambient conditions,with a particular focus on the progress of CO_(2)RR electrocatalyst engineering and reactor design.Our discussion begins with three types of electrocatalysts for CO_(2)RR(noble metalbased,none-noble metal-based,and metal-free electrocatalysts),and then we examine systems-level strategies toward engineering specific components of the electrolyzer,including gas diffusion electrodes,electrolytes,and polymer electrolyte membranes.We close with future perspectives on catalyst development,in-situ/operando characterization,and electrolyzer performance evaluation in CO_(2)RR studies.

Revealing the GHG reduction potential of emerging biomass-based CO_(2) utilization with an iron cycle system

CO_(2) utilization becomes a promising solution for reducing anthropogenic greenhouse gas (GHG) emissions. Biomass-based CO_(2) utilization (BCU) even has the potential to generate negative emissions, but the corresponding quantitative evaluation is limited. Herein, the biomass-based CO_(2) utilization with an iron cycle (BCU-Fe) system, which converts CO_(2) into formate by Fe under hydrothermal conditions and recovers Fe with biomass-derived glycerin, was investigated. The GHG reduction potential under various process designs was quantified by a multidisciplinary method, including experiments, simulations, and an ex-ante life-cycle assessment. The results reveal that the BCU-Fe system could bring considerable GHG emission reduction. Significantly, the lowest value is −34.03 kg CO_(2)-eq/kg absorbed CO_(2) (−2.44 kg CO_(2)-eq/kg circulated Fe) with the optimal yield of formate (66%) and Fe (80%). The proposed ex-ante evaluation approach not only reveals the benefits of mitigating climate change by applying the BCU-Fe system, but also serves as a generic tool to guide the industrialization of emerging carbon-neutral technologies.

Revealing the anti-sintering phenomenon on silica-supported nickel catalysts during CO_(2)hydrogenation

The CO_(2)catalytic hydrogenation represents a promising approach for gas-phase CO_(2)utilization in a direct manner.Due to its excellent hydrogenation ability,nickel has been widely studied and has shown good activities in CO_(2)hydrogenation reactions,in addition to its high availability and low price.However,Ni-based catalysts are prone to sintering under elevated temperatures,leading to unstable catalytic performance.In the present study,various characterization techniques were employed to study the structural evolution of Ni/SiO_(2)during CO_(2)hydrogenation.An anti-sintering phenomenon is observed for both 9%Ni/SiO_(2)and 1%Ni/SiO_(2)during CO_(2)hydrogenation at 400℃.Results revealed that Ni species were re-dispersed into smaller-sized nanoparticles and formed Ni^(0)active species.While interestingly,this anti-sintering phenomenon leads to distinct outcomes for two catalysts,with a gradual increase in both reactivity and CH_(4)selectivity for 9%Ni/SiO_(2)presumably due to the formation of abundant surface Ni°from redispersion,while an apparent decreasing trend of CH_(4)selectivity for 1%Ni/SiO_(2)sample,presumably due to the formation of ultra-small nanoparticles that diffuse and partially filled the mesoporous pores of the silica support over time.Finally,the redispersion phenomenon was found relevant to the H_(2)gas in the reaction environment and enhanced as the H_(2)concentration increased.This finding is believed to provide in-depth insights into the structural evolution of Ni-based catalysts and product selectivity control in CO_(2)hydrogenation reactions.

Catalytic Conversion of CO2 to Cyclic Carbonates through Multifunctional Zinc-Modified ZSM-5 Zeolitet

The production of fine chemicals using CO2 as C1 building block through inexpensive heterogeneous catalysts with high efficiency under low pressure is challenging. Herein we propose for the first time the utilization of a multifunctional heterogeneous zinc-modified HZSM-5 （ZnHZSM-5） catalyst for upgrading CO2 by incorporation into cyclic carbonates from CO2 and epoxides. Owing to the nice surface properties such as abundant Lewis acid, Bronsted acid and Lewis base sites, large surface area, and plenty of micropores, CO2 could be concentrated and well activated in ZnHZSM-5 verified by CO2-TPD, TG-MS, etc. Meanwhile, the epoxides were also activated through metal center and hydrogen bond. Therefore, the reaction can easily assemble at the catalyst interface and show exceptional performance, affording the aimed products with high yield of up to 99% in the presence of commercial tetra-n-propylammonium bromide （90% in kilogram scale with 0.004 mol% ZnHZSM-S and 0.03.5 mol% n^Pr4NBr）.

Upgrading CO2 by Incorporation into Urethanes through Silver-Catalyzed One-Pot Stepwise Amidation Reaction

One-pot two-step stepwise reaction of terminal propargylic alcohols, carbon dioxide, and primary/secondary amines for the effective synthesis of various urethanes through robust silver-catalysed C-O/C-N bond formation is reported, Catalytic activities were investigated by controlling catalyst loading, reaction pressure and time, and very high turnover number （turnover frequency） was obtained： 3350 （35 h-1） with 0.01 mol% silver catalyst under 0.1 MPa, and up to 13360 （139 h-1） with 0.005 mol% silver catalyst under 2.0 MPa at room temperature. The strategy was ingeniously regulated, and synchronously afforded a wide range of β-oxopropylcarbamate and 1,3-oxazolidin-2-one motifs in excellent yields and selectivity together with unprecedented high turnover number （TON） and turnover frequency （TOF） value.

Spirocyclizative Remote Arylcarboxylation of Nonactivated Arenes with CO_(2) via Visible-Light-Induced Reductive Dearomatization

Visible-light-induced reductive dearomatization of nonactivated arenes is a very challenging transformation and remains in its infancy.Herein,we report a novel strategy to achieve a visible-light-induced spirocyclizative remote arylcarboxylation of nonactivated arenes including naphthalenyl-and phenyl-bearing aromatics with CO_(2) under mild conditions through a radical-polar crossover cascade(RPCC).This reductive dearomatization protocol rapidly delivers a broad range of spirocyclic and valuable carboxylic acid derivatives from readily accessible aromatic precursors with generally good regioselectivity and chemoselectivity.