Active Centers Of Catalyst Research Articles

Catalytic degradation of stable benzene molecules under room temperature conditions over Pt-loaded boron-carbon-nitride (Pt/BCN) catalysts

The catalytic degradation of volatile organic compounds (VOCs) such as benzene via ring-opening at room temperature is challenging due to the presence of π-bonds in the ring-forming carbon atoms. This study involved the preparation of a novel Pt-loaded boron-carbon-nitride (Pt/BCN) catalyst containing single-atom active sites for efficient catalysis of benzene degradation at room temperature in air. The micromorphology, surface structure, and coordination environment of the catalyst were analyzed using characterization techniques including aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC–HAADF–STEM) and X-ray absorption fine structure (XAFS). The degradation mechanism was investigated using electron paramagnetic resonance (EPR) and in situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS). The experimental results demonstrate that Pt/BCN contains many Pt-N4 single-atom active sites that can generate hydroxyl radicals under room-temperature air conditions, leading to the oxidation of benzene to CO2 and H2O. Containing atomically dispersed active-site catalysts developed in this study offer a theoretical foundation for designing catalyst active centers in related fields and advancing the industrial application of room-temperature, low-carbon VOCs treatment technologies.

Highly efficient activation of peroxymonosulfate via KOH-activated Fe@NC for the degradation of bisphenol A.

In this study, the KOH-modified Fe-ZIF-derived carbon materials (Fe@NC-KOH-x) were designed for Fenton-like systems to enhance bisphenol A (BPA) removal from wastewater. Compared with the Fe@NC without KOH activation, the pore structure, BET (Brunner-Emmet-Teller) surface area, and oxygen-containing functional group of KOH-activated Fe@NC-KOH-x are dramatically improved, which increases the adsorption and catalytic performance. The Fe@NC-KOH-900/PMS system showed significant BPA removal reactivity across wide pH ranges and low doses of Fe@NC-KOH-900. Interestingly, our findings indicated that the removal effectiveness of BPA improved when PMS was introduced following the saturation adsorption of Fe@NC-KOH-x, as compared to the simultaneous introduction of Fe@NC-KOH-x and PMS. More particularly, through regression analysis, we found that the proportion of reactive species in the Fe@NC-KOH-x/PMS system changes with the increase of pyrolysis temperature, and there was a certain relationship between structure-function and active species in the Fe@NC-KOH-x/PMS system. O-C = O, Fe-N4, C-O, and pyrrolic N in Fe@NC-KOH-x lead to the generation of •OH, and SO4-•, C = O, Fe-N4, and defect are closely related to FeIV = O, and the formation of 1O2 is affected by Fe-N4, graphite N, C = O, and defect. Also, the density functional theory (DFT) calculation and the potential correlation between catalyst active centers and reactive oxygen species indicate that Fe-N4 is the main active site of Fe@NC-KOH-x. These outcomes of the study offer an innovation for enhanced elimination of BPA in wastewater treatment and provide a dynamic understanding of the mechanism of BPA degradation.

Polymeric Catalyst with Discrete Distributed Active Centers for Regulating Backbone Structure of Poly(propylene carbonate)†

Comprehensive SummaryConverting CO2 into valuable chemicals is an effective means to alleviate environmental pressure and the depletion of oil resources. Among them, polymers derived from the copolymerization of PO and CO2 have been widely studied because of their excellent properties. To meet the expansion of the application range of CO2‐based polymers, regulation of the CU in the polymer is imperative. Based on the understanding of the relationship between catalyst synergy and structure, we designed a new generation of polyester‐based polymeric catalysts APEPC‐R and RPEPC‐N with discretely distributed active centers to achieve the synthesis of CO2‐based polymers with regulated CU (from 50% to 90%). The discrete arrangement of catalyst active centers was demonstrated by 1H NMR and UV‐vis characterization. Benefiting from multi‐site synergy, high molecular weight (Mn > 100 kg/mol) CO2‐based copolymers with CU among 50%—90% were successfully synthesized and their properties were firstly investigated. This work not only contributes to enriching the scope of the application of CO2‐based copolymers but also provides a new platform for the development of a new generation of catalysts.

Acceptorless ambient-temperature dehydrogenation and reversible hydrogenation of N-heterocycles over single-atom Co-N-C catalysts

Reversible hydrogen storage via Liquid organic hydrogen carriers (LOHCs) is one of the key technologies for efficient utilization of hydrogen energy. How to construct efficient dehydrogenation/hydrogenation catalysts that enable low-temperature catalysis still remains challenging. Herein, we present the design and construction of single-atom Co-N-C(x) catalysts allowing significantly improved acceptorless dehydrogenation of 1,2,3,4-tetrahydroquinoline (THQ). By varying the ligand/Co ratio, the optimal Co-N-C(1.5) can achieve 97.5% dehydrogenated product and 0.82 h−1 TOF value at ambient temperature, overperforming many reported non-noble metal even noble metal catalysts. This catalyst exhibits good recyclability and substrate versatility, enabling ambient temperature dehydrogenation of various N-heterocycles and efficient reverse hydrogenation of aromatic N-heterocycles, thus achieving the loop of reversible hydrogen storage. The active catalyst centers consist of specific Co-Nx moieties and nitrogen species within the carbon support. Controlled experiments reveal that the different performance of Co-N-C(x) is determined by density of the Co-Nx, and the rate-determining step of THQ dehydrogenation is correlated with the bond cleavages in surface-bound THQ. This work offers a promising pathway for energy-efficient and cost-effective hydrogen energy utilization under practical conditions.

Sorption-enhanced Fischer-Tropsch synthesis – Effect of water removal

The Sorption-Enhanced Fischer-Tropsch synthesis (SEFTS), with water removal by means of a solid sorbent, has been demonstrated for the first time experimentally. Commercial water sorbents (Zeolites type 13X and 4 A) were thoroughly characterized to determine water sorption capacity at relevant temperatures (100–250°C) as well as multicycle stability after 100 cycles at 210°C. The adsorption capacity of both zeolties decreased with increasing temperature. The adsorption capacity of 4 A remained almost constant after 100 adsorption/desorption cycles, while 13X lost almost 50% of its capacity. Post characterization of the 13X sample showed distorted crystallinity after 100 cycles which explains the drop in stability. The SEFTS experiments were performed as a cyclic operation, first FT reaction and then water sorbent regeneration, at 210 °C and 5 bar. The system with zeolites showed 10% higher CO conversion after 65 hours on stream compared to the system without any sorbents. The selectivities to C5+ was higher for the system with sorbents compared to the system without zeolites. A much steeper deactivation curve was also observed for the system without zeolites at steady state conditions. This might be due to the fact that zeolites adsorbs the water and remove it from the catalyst active centers, thus increase catalyst stability by preventing the catalyst re-oxidation. Overall, this work opens an opportunity for enhancing the catalyst activity in FTS by in situ water sorption.

Regulating Ru−O Bonding Interactions by Ir Doping Boosts the Acid Oxygen Evolution Performance

AbstractHighly active and stable oxygen evolution reaction (OER) catalysts are crucial for the large‐scale application of proton exchange membrane water electrolyzers. However, the dynamic reconfiguration of the catalyst surface structure and active centers is still undefined, which greatly hinders the development and application of efficient OER catalysts. Herein, we report an Ir0.3Ru0.7Ox/C catalyst with a facile low‐temperature synthesis route, which can reach 10 mA cm−2 at an overpotential of 217 mV with a Tafel slope as low as 39.4 mV dec−1, and yields a mass activity 61 times that of commercial IrO2/C at an overpotential of 300 mV. The lattice oxygen structure of RuOx is stabilized by the introduction of Ir species, thus greatly promoting the OER activity and durability. Further in situ Raman reveals that RuOx emerges as the active species at high potentials, and Ru−O bonding interactions are enhanced with Ir regulation, stabilizing the solvation of Ru at high potentials and accelerating the nucleophilic attack of water molecules, leading to the improved OER performance. This work deepens the fundamental understanding of OER and offers an effective way to advance the utilization of Ru‐based OER catalysts.

Evolution of high spin state single-atom catalyst active centers in Na–O2 batteries

Compared to O2@MN4, O2@MN3 with high spin state favors side-on mode, which enhances the coupling between 3dxy orbital of metal and O2, hence causes the evolution of active center from MN3 to (OMO)N3, and increases the performance of Na–O2 batteries.

Insights into the differences in metal anchoring mechanisms and the impact on HCN catalytic oxidation performance

Hydrogen cyanide (HCN) is often produced in various industrial processes, such as metal smelting, carbon fiber production, etc. Due to its highly toxic nature, it has significant harm to the human body and the environment. Catalytic oxidation can convert HCN into non-toxic N2, CO2 and H2O. In this study, we conducted a comparative evaluation of the catalytic oxidation of HCN using Cu, Co and Mn as catalyst active centers, and used in situ DRIFTS to explore the reaction mechanism of HCN catalytic oxidation. The difference in the anchoring state of different metals on the hydroxyl groups on the Al2O3 surface, mainly the difference in anchoring strength and hydroxyl consumption, determines the difference in the metal dispersion state, which in turn affects the oxygen activation ability and HCN oxidation performance. Under high loading conditions, compared to Co and Mn, Cu species are more fully anchored due to lower hydroxyl consumption, exhibiting higher dispersion and redox properties, so the 10Cu/Al2O3 catalyst performs well HCN oxidation activity.

Atomically Dispersed Cobalt/Copper Dual-Metal Catalysts for Synergistically Boosting Hydrogen Generation from Formic Acid.

The development of practical materials for (de)hydrogenation reactions is a prerequisite for the launch of a sustainable hydrogen economy. Herein, we present the design and construction of an atomically dispersed dual-metal site Co/Cu-N-C catalyst allowing significantly improved dehydrogenation of formic acid, which is available from carbon dioxide and green hydrogen. The active catalyst centers consist of specific CoCuN6 moieties with double-N-bridged adjacent metal-N4 clusters decorated on a nitrogen-doped carbon support. At optimal conditions the dehydrogenation performance of the nanostructured material (mass activity 77.7 L ⋅ gmetal -1 ⋅ h-1 ) is up to 40 times higher compared to commercial 5 % Pd/C. In situ spectroscopic and kinetic isotope effect experiments indicate that Co/Cu-N-C promoted formic acid dehydrogenation follows the so-called formate pathway with the C-H dissociation of HCOO* as the rate-determining step. Theoretical calculations reveal that Cu in the CoCuN6 moiety synergistically contributes to the adsorption of intermediate HCOO* and raises the d-band center of Co to favor HCOO* activation and thereby lower the reaction energy barrier.

Selective hydrogenation of carbon–carbon double bond catalyzed by FLP-MOFs

Selective hydrogenation of CC double bond in α, β-unsaturated carbonyl compounds is of great significance in the production of fine chemicals, and the design and preparation of hydrogenation catalysts with high selectivity is the key to realize the industrialization of this reaction. Controlling and adjusting the steric hindrance between substrate molecules and active center of catalysts is an effective strategy to achieve high selectivity. In this work, the spatially hindered “Frustrated Lewis pairs” (FLPs) was used as the active component and metal-organic frameworks (MOFs) materials with a certain window size were used as the catalyst support. We designed and synthesized a heterogeneous hydrogenation catalyst B(C6F5)3/DO-MIL-101 by immobilizing FLP onto metal-organic frameworks (MIL-101). Characterizations and catalytic performance tests revealed that the catalytically active species B(C6F5)3/DO was confined in MIL-101 nanocavities via Cr–O coordination bond. The resulting B(C6F5)3/DO-MIL-101 catalyst not only realized the recycling of FLP, but also showed excellent catalytic activity and high selectivity in the selective hydrogenation of CC double bond in α, β-unsaturated carbonyl ketones. It should be noted that the steric hindrance between FLP and substrate molecules, as well as the shape selectivity of MOFs nanocages, are the principal factors for the high selectivity of the catalyst.

Marriage of Ultralow Platinum and Single-Atom MnN4 Moiety for Augmented ORR and HER Catalysis

Hitherto, Pt-based catalysts still are state of the art for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER), but high dosage, low atom-utilization efficiency, and uncontrollable size of Pt species seriously impede their applications. Given this, we propose an effective way by enhancing Pt–transition metal single-atom interaction. Due to the strong interaction between single-atom Mn sites in Mn–N–C and Pt species, the overgrowth of Pt species is effectively limited with an average size smaller than 2.5 nm. Meanwhile, the regulated electronic structure drives electron transfer from Mn to adjacent Pt sites, endowing catalysts with reduced reaction energy barrier and higher intrinsic activity. As expected, the obtained Pt@Mn-SAs/N-C nanocatalyst with ideal Pt size and ultralow Pt loading (1.98 wt %) exhibits extraordinarily high ORR mass activity at 0.9 V in acidic and alkaline media, which is 11.1 and 14.7 times larger than that of commercial Pt/C, respectively. Moreover, at 30 mV, its HER mass activity is even 33.4 and 18.7 times larger than that of Pt/C. Theory calculation results show that favorable charge density rearrangement and resulting electron-enriched Pt sites, with negatively shifted d-band centers, weaken surface adsorption of key intermediates, boosting ORR/HER activity. This work provides enlightenment for integration of multiple active centers in catalysts.

Mastering the D-Band Center of Iron-Series Metal-Based Electrocatalysts for Enhanced Electrocatalytic Water Splitting

The development of non-noble metal-based electrocatalysts with high performance for hydrogen evolution reaction and oxygen evolution reaction is highly desirable in advancing electrocatalytic water-splitting technology but proves to be challenging. One promising way to improve the catalytic activity is to tailor the d-band center. This approach can facilitate the adsorption of intermediates and promote the formation of active species on surfaces. This review summarizes the role and development of the d-band center of materials based on iron-series metals used in electrocatalytic water splitting. It mainly focuses on the influence of the change in the d-band centers of different composites of iron-based materials on the performance of electrocatalysis. First, the iron-series compounds that are commonly used in electrocatalytic water splitting are summarized. Then, the main factors affecting the electrocatalytic performances of these materials are described. Furthermore, the relationships among the above factors and the d-band centers of materials based on iron-series metals and the d-band center theory are introduced. Finally, conclusions and perspectives on remaining challenges and future directions are given. Such information can be helpful for adjusting the active centers of catalysts and improving electrochemical efficiencies in future works.

Activated Ni-O-Ir Enhanced Electron Transfer for Boosting Oxygen Evolution Reaction Activity of LaNi1-x Irx O3.

Tuning the structure of the active center of catalysts to atomic level provides the most efficient utilization of the active component, which plays an especially important role for precious metals. In this study, the liquid phase ion exchange method is used to introduce atomic Ir into LaNiO3 perovskite oxide, which shows excellent catalytic performance in the oxygen evolution reaction (OER). The catalyst, LaNi0.96 Ir0.04 O3 , with the optimal concentration of Ir, displays an overpotential of just 280mV at 10mAcm-2 . The introduced Ir enriches the surface electron density significantly, which not only improves site-to-site electron transfer between O and Ni sites but also allows stable adsorption of the intermediates. Theresults of cyclic voltammetry tests reveal the superior overpotential and remarkable efficiency of the OER process because of the strong interactions in Ni-O-Ir. Moreover, the Ir atom inhibits the participation of a lattice oxygen oxidation mechanism (LOM) in LaNiO3 that guarantees the stability of the catalyst in alkaline conditions. It is anticipated that this work will be instrumental for the preparation and study of a broad range of atomic metal-doped perovskite oxides for water splitting.

Engineering of Nanostructured Carbon Catalyst Supports for the Continuous Reduction of Bromate in Drinking Water

Recent works in the development of nanostructured catalysts for bromate reduction in drinking water under hydrogen have highlighted the importance of the properties of the metallic phase support in their overall performance. Since most works in catalyst development are carried out in powder form, there is an overlooked gap in the correlation between catalyst support properties and performance in typical continuous applications such as fixed bed reactors. In this work, it is shown that the mechanical modification of commercially available carbon nanotubes, one of the most promising supports, can significantly enhance the activity of the catalytic system when tested in a stirred tank reactor, but upon transition to a fixed bed reactor, the formation of preferential pathways for the liquid flow and high pressure drops were observed. This effect could be minimized by the addition of an inert filler to increase the bed porosity; however, the improvement in catalytic performance when compared with the as-received support material was not retained. The operation of the continuous catalytic system was then optimized using a 1 wt.% Pd catalyst supported on the as-received carbon nanotubes. Effluent and hydrogen flow rates as well as catalyst loadings were systematically optimized to find an efficient set of parameters for the operation of the system, regarding its catalytic performance, capacity to treat large effluent flows, and minimization of catalyst and hydrogen requirements. Experiments carried out in the presence of distilled water as a reaction medium demonstrate that bromate can be efficiently removed from the liquid phase, whereas when using a real water matrix, a tendency for the deactivation of the catalyst over time was more apparent throughout 200 flow passages over the catalytic bed, which was mostly attributed to the competitive adsorption of inorganic matter on the catalyst active centers, or the formation of mineral deposits blocking access to the catalyst.

SO2 Poisoning Mechanism of the Multi-active Center Catalyst for Chlorobenzene and NOx Synergistic Degradation at Dry and Humid Environments.

The performance of fresh (PdV/TiO2), sulfur poisoned (Used-S and Used-H), and regenerated (Used-RS and Used-RH) multi-active center catalysts for chlorobenzene catalytic oxidation and selective catalytic reduction (CBCO + SCR) reaction is investigated. The reaction on the catalyst surface is blocked after sulfur poisoning owing to the occupation and deposition of catalyst active centers (mainly Pd centers) by PdSO4 (and/or PdS in a dry environment) and NH4HSO4 species, especially the CBCO process. Sulfates (mainly NH4HSO4) on the sulfur poisoned catalyst surface are partially decomposed after 400 °C thermal regeneration, while the deactivation caused by the formation of PdSO4 species is irreversible. Density functional theory calculation results show that in the PdSO4 and NH4HSO4 generation paths, each step of the elementary reaction has just a small energy barrier to overcome, and the stability of the product for each elementary reaction increases gradually. Even worse, SO2 is easily combined with H2O gas molecules to form H2SO3 in a humid environment, and the energy barrier for conversion of SO32- to SO42- is just 0.041 eV. The two oxygen vacancies (VOx-1 or TiOx-1) provide adsorption sites for CBCO + SCR reaction gas molecules but do not exhibit adsorption properties for SO2, which gives a possible idea for optimization of sulfur resistance. The present work is favorable for further synergistic removal of CB/NOx by the catalyst for anti-SO2 poisoning modification and application in the manufacture industry.

DNA-Modified Cobalt Tungsten Oxide Hydroxide Hydrate Nanochains as an Effective Electrocatalyst with Amplified CO Tolerance during Methanol Oxidation.

Direct methanol fuel cell technology implementation mainly depends on the development of non-platinum catalysts with good CO tolerance. Among the widely studied transition-metal catalysts, cobalt oxide with distinctively higher catalytic efficiency is highly desirable. Here, we have evolved a simple method of synthesizing cobalt tungsten oxide hydroxide hydrate nanowires with DNA (CTOOH/DNA) and without incorporating DNA (CTOOH) by microwave irradiation and subsequently employed them as electrocatalysts for methanol oxidation. Following this, we examined the influence of incorporating DNA into CTOOH by cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. The enhanced electrochemical surface area of CTOOH offered readily available electroactive sites and resulted in a higher oxidation current at a lower onset potential for methanol oxidation. On the other hand, CTOOH/DNA exhibited improved CO tolerance and it was evident from the chronoamperometric studies. Herein, we noticed only a 2.5 and 1.8% drop at CTOOH- and CTOOH/DNA-modified electrodes, respectively, after 30 min. Overall, from the results, it was evident that the presence of DNA in CTOOH played an important role in the rapid removal of adsorbed intermediates and regenerated active catalyst centers possibly by creating high density surface defects around the nanochains than bare CTOOH.

Toward Olefin Multiblock Copolymers with Tailored Properties: A Molecular Perspective

AbstractRecent progress in macromolecular reaction engineering has enabled the synthesis of sequence‐controlled polymers. The advent of olefin block copolymers (OBCs) via chain shuttling polymerization of ethylene with α‐olefins has opened new horizons for the synthesis of polyolefins having a dual character of thermoplastics and elastomers. Nevertheless, the use of two catalysts with different comonomer selectivities and a chain shuttling agent, dragging and dropping live chains between active catalyst centers, made precise tailoring of OBCs microstructure containing hard and soft units a feasible challenge. This work discusses the possibility of predicting properties of OBCs from its simulated molecular patterns. The microstructural characteristics of OBCs are discussed in terms of topology‐related and property‐related features. An intelligent tool, which combines the benefits of kinetic Monte Carlo simulation and artificial neural network modeling, is used to explore the connection between polymerization recipe (catalyst composition, ethylene to 1‐octene monomer ratio, and chain shuttling agent level) and topology‐related as well as property‐related microstructural features. The properties of target OBCs are reflected in the hard block percent, the number of 1‐octene units in the copolymer chains, and the longest ethylene sequence length of the hard and soft segments.

Active centers of redox catalysts

The development of representations about the active site structure of solid-phase catalysts, ranging from the work of H. Taylor to a modern understanding of the complex and multi-level structure of catalytic systems, is considered. The main types of active centers of catalysts for redox processes of deep, selective, and preferential conversion are analyzed. It is shown that for each type of reaction, regardless of the chemical nature of the catalyst components, the structure of the active center is characterized by certain common features and determines the direction of conversion. Particular attention is paid to the structure of active sites formed by the type of an isolated active center ("Single Site Isolation"), which allows achieving high selectivity of catalytic processes in the direction of target products obtaining and implementation of new reactions. In particular, the reaction of methane oxidative carbonylation to acetic acid was first carried out in a gas phase using molecular oxygen as an oxidant and catalysts whose active centers were presented by isolated Rh3+ ions in the composition of rhodium selenochloride. A separate type of active center is presented by atoms located on the grain boundaries of crystallites, which arise as a result of interfacing interaction between catalyst components: support, active component, modificator, as well as grain boundaries between homogeneous nanocrystallites in agglomerated systems. It is shown that an important role in the manifestation of catalytic properties plays the availability of an active center for reagents, caused by the spatial structure of catalysts. Zeolites, organometallic compounds (MOF), mesostructural oxides in which active centers are located inside the cavity channels are examples of such catalytic systems. The main strategy of research in the field of advanced catalysts is aimed at developing methods for the synthesis of catalytic materials, which provide formation as the maximum number of active centers, so their availability for reagents and subsequent conversion to target products. Designing such systems is a complex task, based on establishing a correlation between composition, structure, and size characteristics of catalytic materials.

Boost oxygen reduction reaction performance by tuning the active sites in Fe-N-P-C catalysts

Cost-effective atomically dispersed Fe-N-P-C complex catalysts are promising to catalyze the oxygen reduction reaction (ORR) and replace Pt catalysts in fuel cells and metal-air batteries. However, it remains a challenge to increase the number of atomically dispersed active sites on these catalysts. Here we report a highly efficient impregnation-pyrolysis method to prepare effective ORR electrocatalysts with large amount of atomically dispersed Fe active sites from biomass. Two types of active catalyst centers were identified, namely atomically dispersed Fe sites and FexP particles. The ORR rate of the atomically dispersed Fe sites is three orders of magnitude higher than it of FexP particles. A linear correlation between the amount of the atomically dispersed Fe and the ORR activity was obtained, revealing the major contribution of the atomically dispersed Fe to the ORR activity. The number of atomically dispersed Fe increases as the Fe loading increased and reaching the maximum at 1.86 wt% Fe, resulting in the maximum ORR rate. Optimized Fe-N-P-C complex catalyst was used as the cathode catalyst in a homemade Zn-air battery and good performance of an energy density of 771 Wh kgZn−1, a power density of 92.9 mW cm−2 at 137 mA cm−2 and an excellent durability were exhibited.

Reaction mechanism of CO2 methanation over Rh/TiO2 catalyst

Rh/TiO2 has been regarded as a very promising catalyst for the low-temperature CO2 methanation. However, the atomic-level reaction mechanism that dictates the reactivity and selectivity of CO2 reduction over Rh/TiO2 catalyst remains elusive. The reaction mechanism governed by a delicate interplay of surface reaction chemistry and thermodynamics was systematically investigated using density functional theory calculations. Theoretical results indicate that significant charges accumulate at the perimeter of the interface between support TiO2 and Rh nanoparticle. Metal-support interface is identified as the most active site for CO2 adsorption and activation over Rh/TiO2 catalyst. Compared with the direct C–O bond cleavage pathway and formate pathway, the reverse water–gas shift (RWGS) reaction followed by CO hydrogenation is much more thermodynamically and kinetically favorable for CO2 methanation over Rh/TiO2 catalyst. The RWGS + CO hydrogenation pathway via H2COH* dissociation dominates CO2 methanation due to the relatively lower energy barrier. CO2 methanation via the RWGS + CO hydrogenation pathway prefers to proceed through the channel: CO2* → COOH* → CO* → COH* → HCOH* → H2COH* → CH3* → CH4*. H-assisted COOH* dissociation is identified as the rate-determining step of CO2 methanation over Rh/TiO2 catalyst. Finally, a reaction network is established to understand the atomic-level reaction mechanism of CO2 methanation over Rh/TiO2 catalyst. These mechanistic insights can guide the rational design of catalyst active centers to boost the activity and selectivity of CO2 reduction.