High Catalyst Loading Research Articles

Spectroscopy vs. Electrochemistry: Catalyst Layer Thickness Effects on Operando/In Situ Measurements

AbstractIn recent years, operando/in situ X‐ray absorption spectroscopy (XAS) has become an important tool in the electrocatalysis community. However, the high catalyst loadings often required to acquire XA‐spectra with a satisfactory signal‐to‐noise ratio frequently imply the use of thick catalyst layers (CLs) with large ion‐ and mass‐transport limitations. To shed light on the impact of this variable on the spectro‐electrochemical results, in this study we investigate Pd‐hydride formation in carbon‐supported Pd‐nanoparticles (Pd/C) and an unsupported Pd‐aerogel with similar Pd surface areas but drastically different morphologies and electrode packing densities. Our in situ XAS and rotating disk electrode (RDE) measurements with different loadings unveil that the CL‐thickness largely determines the hydride formation trends inferred from spectro‐electrochemical experiments, therewith calling for the minimization of the CL‐thickness in such experiments and the use of complementary thin‐film control measurements.

Spectroscopy vs. Electrochemistry: Catalyst Layer Thickness Effects on Operando/In Situ Measurements.

In recent years, operando/in situ X-ray absorption spectroscopy (XAS) has become an important tool in the electrocatalysis community. However, the high catalyst loadings often required to acquire XA-spectra with a satisfactory signal-to-noise ratio frequently imply the use of thick catalyst layers (CLs) with large ion- and mass-transport limitations. To shed light on the impact of this variable on the spectro-electrochemical results, in this study we investigate Pd-hydride formation in carbon-supported Pd-nanoparticles (Pd/C) and an unsupported Pd-aerogel with similar Pd surface areas but drastically different morphologies and electrode packing densities. Our in situ XAS and rotating disk electrode (RDE) measurements with different loadings unveil that the CL-thickness largely determines the hydride formation trends inferred from spectro-electrochemical experiments, therewith calling for the minimization of the CL-thickness in such experiments and the use of complementary thin-film control measurements.

Synthesis of Catalyst Using Bio‐benign Precursors and Its Application in One‐Pot Catalytic Synthesis of Imidazo[1,2‐a]pyridines

AbstractDevelopment of catalysts using natural feedstock is the need of the current era, and accordingly, we have developed a new ligand N‐(2‐hydroxynapthylidene)‐L‐leucienyl‐4,6‐O‐ethylidene‐β‐D‐glucopyranosylamine using natural occurring D‐glucose and L‐amino acid. It interacts with several bio‐relevant metal ions like iron, copper, zinc, etc., but its association with cupric ions is immune to pH (4.2–9.1) change. In‐situ copper‐catalyzed reactions have been proven to be pivotal in many important organic syntheses, including imidazo[1,2‐a]pyridines, which is one of the important precursors of many drug molecules. Catalytic synthesis of imidazo[1,2‐a]pyridines requires high catalyst loading, hazardous solvent, high temperature, and long reaction time, which are major drawbacks towards green synthetic methodology. Interestingly, our glycoconjugate‐derived cupric complex catalyzes the reactions among aldehydes, 2‐aminopyridines, and terminal alkynes under the solvent‐free condition to afford one‐pot synthesis of imidazo[1,2‐a]pyridines and 23 derivatives have been reported in good to excellent yields (53–93 %) using lower reaction time, temperature, and catalyst loading compared to other reports on similar reactions. Hence, our approach enhances the green methodology towards the catalytic synthesis of imidazo[1,2‐a]pyridine derivatives.

Enhanced Carbon Monoxide Electroreduction to >1 A cm−2 C2+ Products Using Copper Catalysts Dispersed on MgAl Layered Double Hydroxide Nanosheet House‐of‐Cards Scaffolds

AbstractCu catalysts are most apt for reducing CO(2) to multi‐carbon products in aqueous electrolytes. To enhance the product yield, we can increase the overpotential and the catalyst mass loading. However, these approaches can cause inadequate mass transport of CO(2) to the catalytic sites, which will then lead to H2 evolution dominating the product selectivity. Herein, we use a MgAl LDH nanosheet ‘house‐of‐cards’ scaffold to disperse CuO‐derived Cu (OD‐Cu). With this support‐catalyst design, at −0.7 VRHE, CO could be reduced to C2+ products with a current density (jC2+) of −1251 mA cm−2. This is 14× that of the jC2+ shown by unsupported OD‐Cu. The current densities of C2+ alcohols and C2H4 were also high at −369 and −816 mA cm−2 respectively. We propose that the porosity of the LDH nanosheet scaffold enhances CO diffusion through the Cu sites. The CO reduction rate can thus be increased, while minimizing H2 evolution, even when high catalyst loadings and large overpotentials are used.

Enhanced Carbon Monoxide Electroreduction to >1 A cm-2 C2+ Products Using Copper Catalysts Dispersed on MgAl Layered Double Hydroxide Nanosheet House-of-Cards Scaffolds.

Cu catalysts are most apt for reducing CO(2) to multi-carbon products in aqueous electrolytes. To enhance the product yield, we can increase the overpotential and the catalyst mass loading. However, these approaches can cause inadequate mass transport of CO(2) to the catalytic sites, which will then lead to H2 evolution dominating the product selectivity. Herein, we use a MgAl LDH nanosheet 'house-of-cards' scaffold to disperse CuO-derived Cu (OD-Cu). With this support-catalyst design, at -0.7 VRHE , CO could be reduced to C2+ products with a current density (jC2+ ) of -1251 mA cm-2 . This is 14× that of the jC2+ shown by unsupported OD-Cu. The current densities of C2+ alcohols and C2 H4 were also high at -369 and -816 mA cm-2 respectively. We propose that the porosity of the LDH nanosheet scaffold enhances CO diffusion through the Cu sites. The CO reduction rate can thus be increased, while minimizing H2 evolution, even when high catalyst loadings and large overpotentials are used.

Zwitterionic Halido Cyclopentadienone Iron Complexes and Their Catalytic Performance in Hydrogenation Reactions.

The zwitterionic halido cyclopentadienone iron complexes FeX(CO)2-NMe3 (X = Cl, Br, I) were prepared and characterized by NMR, XRD, MS, IR, and elemental analysis. Their catalytic performance in hydrogenation and transfer hydrogenation was assessed. Transfer hydrogenation in boiling iPrOH with acetophenone as the test substrate showed no conversion with FeI(CO)2-NMe3. Hydrogenation reactions under H2 pressure (7.5 bar) in water as solvent showed up to 93% conversion with FeI(CO)2-NMe3 (2.5 mol %) using acetophenone as the test substrate. The overall relative reactivity order was established to be Cl < Br < I, reflecting the relative bond strengths of the Fe-X bonds. Although the compounds presented in this study can be used as precatalysts for hydrogenation reactions in water, the need to employ high temperatures, leading to more catalyst decomposition, as evidenced by pressurized sample infusion-electrospray ionization-mass spectrometry (PSI-ESI-MS), and high catalyst loading limits their usefulness as catalysts. The limit can be circumvented in part by salt effects analogous to those in classical solvolysis chemistry.

Crowded supported metal atoms on catalytically active supports may compromise intrinsic activity: A case study of dual-site Pt/α-MoC catalysts

Increasing the surface population of supported catalytic sites, assuming these sites are stable, is considered a straightforward approach to improving the overall catalytic performance. We report an exception represented by the Pt/α-MoC catalysts featuring atomically dispersed Pt. The Pt/α-MoC catalysts display very high activity for the reverse water gas shift reaction with near 100% CO selectivity for CO2:H2 ratios from 0.25 to 4 and from 250 to 400 °C. Despite the excellent performance, the intrinsic activity per Pt-centric catalytic center declines as the Pt loading increases from 0.1 to 1.0 wt%. With the dispersed Pt evolving from isolated atoms to fully exposed ensembles, the shrinking inter-Pt-atom space impedes CO2 activation at the critical Pt-Mo interfaces, where the Pt shall temporarily take the -O intermediates. The Pt, even as atomically dispersed without noticeable sintering, is underutilized in such a crowded state. This caution for high-loading catalyst design is translational to other systems where the direct catalytic roles of the supports are crucial.

Rotating disk electrode measurements on low and high loading catalyst layers: Diffusion limitations and application to Pt catalysts supported on porous micrometric carbon xerogel particles designed for proton exchange membrane fuel cells

Innovative fuel cell catalysts are now often being supported on nanostructured materials in order to improve mass transport, contact with the ionomer and active phase distribution. However, to maintain their inner structure, these supports are used as µm-sized particles, which hampers to perform accurate kinetic experiments on rotating disk electrode since a thin layer of catalyst is in principle required. The present study thus aims at checking if accurate measurements remain possible for thick layers of large particles. To do so, oxygen reduction was first performed on a commercial Pt catalyst supported on carbon black; both a typical thin and a thick layer (37 and 370 µgPt cm−2) were used. The impact of the diffusion limitations on the kinetic current was determined. The same measurement protocol was then performed with a catalyst supported on 5 µm particles of a nanostructured carbon (∼15 µm layer thickness, 370 µgPt cm−2). Results and calculation show that, for both thick layers, the kinetic current should be measured at higher potential (1.00 or 1.05 V/ESH) than usual to avoid diffusion limitations. Also, the voltage scanning rate should be lowered to 0.5 or 1 mV s−1 to decrease the impact of the double layer capacity on the measurements.

A Multifunctional Biomass Zinc Catalyst for Epoxy-Based Vitrimers and Composites

High catalyst loading is often required in the preparation of epoxy-based vitrimers. This may lead to catalyst migration, pollution, and a decrease in mechanical properties. In this contribution, a biomass zinc carboxylate (EP-Zn) derived from the epoxide of 10-undecenoic acid is used as a multifunctional catalyst in the synthesis of bisphenol A-epoxy-based vitrimers. The zinc ions can catalyze curing, transesterification and hydrolysis (degradation) reactions of polyester epoxy resins. More importantly, the zinc carboxylate no longer exists in the free state but becomes part of the crosslinked network, leading to significant enhancement of the tensile properties via the formation of supramolecular ionic clusters. Moreover, the amphiphilic structure of this long-chain zinc carboxylate allows it to be used as a compatibilizer for vitrimer-based composites, enabling improved tensile strength.

Impact of catalyst loading of atomically dispersed transition metal catalysts on H2O2 electrosynthesis selectivity

Electrosynthesis of hydrogen peroxide (H2O2) via a two-electron oxygen reduction reaction (2e− ORR) has emerged as a promising alternative to the current anthraquinone process. Atomically dispersed transition metal catalysts (M–N/C catalysts; M=transition metal) have received particular attention as H2O2 electrosynthesis catalysts. Among the factors affecting catalytic properties, the catalyst loading on the electrode has significant impacts on the ORR activity and selectivity of M–N/C catalysts in particular and electrocatalysts in general. However, the loading effect has been largely neglected and underexplored in literature. In this study, we investigated the impacts of the catalyst loading and the metal center in M–N/C catalysts on the 2e− ORR activity and selectivity. We prepared a series of mesoporous carbons comprising M (Fe, Co, Ni)-based atomically dispersed species, meso‑M–N/C catalysts. At a fixed low catalyst loading, the meso‑Co–N/C and meso‑Ni–N/C catalysts exhibited the best 2e−ORR performance under acidic and alkaline electrolytes, respectively. At high catalyst loadings, the H2O2 production activity of the meso‑Co–N/C catalyst dramatically declined to ∼20% compared to that at the low loading. In the thick catalyst layer, the generated H2O2 is accumulated due to poor mass transport, leading to reduction and/or decomposition. In contrast, the H2O2 synthesis activity meso‑Ni–N/C catalyst was nearly insensitive to the catalyst loading, which can be ascribed to the high porosity and well-developed mesopores of the meso‑Ni–N/C catalyst, promoting mass transport.

Structural optimization of 3D printed SiC scaffold with gradient pore size distribution as catalyst support for methanol steam reforming

Porous ceramic catalyst supports can be used for highly efficient methanol steam reforming (MSR) due to their generally high catalyst loading capacity, large specific surface area, and high chemical stability. This paper presents a novel method to design the SiC scaffolds with optimal pore distribution as catalyst supports to enhance the hydrogen production of MSR microreactors. The structural design of the SiC scaffolds was firstly described, then numerical modeling was developed to study the flow and hydrogen production performances of the supports and adopt the steepest ascent method to optimize the pore size distribution of the supports. Then, the optimized SiC supports were printed using direct ink writing of polymer-derived ceramics, then experimental tests were conducted. Both simulation and experimental results showed that the SiC supports with gradient pore size distribution can reduce the pressure drop and improve the methanol conversion rate of the microreactor. Compared with the supports with uniformly distributed pores, the pressure drops of the SiC support with gradient pore size distribution can be reduced by 2.21 % and methanol conversion increased by 13.33 % at inlet flow rate of 40 μl/min and temperature of 280 ℃. This work demonstrated that the potential of using the proposed method to optimize the structural of the catalyst supports for the development of highly efficient MSR microreactors.

Graphite Oxide as a Catalyst for Dehydration of Alcohols

Background: The methods of dehydration of alcohols frequently suffer from the following drawbacks: high reaction temperature, toxic catalysts, high catalyst loading, and difficulty to remove catalysts. Therefore, the development of a new catalyst for the dehydration of alcohols is still of importance. Methods: Graphite oxide is used as a catalyst for dehydration of alcohols. Results: Graphite oxide is used as a catalyst for dehydrating tertiary and secondary alcohols to the corresponding alkenes as well as dehydrating primary alcohols and diols to the corresponding ethers and cycloethers in moderate to excellent conversion rates and good selectivity. Conclusion: In these reactions, GO prepared by the improved Hummers method showed high catalytic activity. As an efficient catalyst, GO is easily available, cheap, weakly acidic with low toxicity, and well tolerant to various functional groups.

Structured sulphur trioxide splitting catalytic systems and allothermally-heated reactors for the implementation of Sulphur-based thermochemical cycles via a centrifugal solar particle receiver

Catalytic sulphur trioxide splitting is the highest-temperature (850–900 °C), endothermic step of several sulphur-based thermochemical cycles targeted to production of hydrogen or solid sulphur. The demonstrated capability of centrifugal particle solar receivers of heating particle streams at such temperatures, can allow for “allothermal” implementation of this step via the enthalpy of such particle streams in a catalytic shell-and-tube reactor/heat exchanger decoupled from a solar receiver. In this context, SO3 splitting catalytic systems shaped to spherical particles and flow-through honeycombs and foams were prepared and tested. Long-term (100–950 h) experiments with catalyst-coated SiC honeycombs demonstrated that oxide-supported Pt catalysts suffered from low conversion and severe deactivation at 650 °C, contrary to Fe2O3-coated ones. Fe2O3-coated SiC foams demonstrated reproducible near-equilibrium conversion at 850 °C, under a broad range of sulphuric acid flow rates, combined with minute pressure drop even under high catalyst loadings (35–45 wt %) being thus in principle suitable for eventual pressurized operation.

Mechanism-Driven Development of Group 10 Metal-Catalyzed Decarbonylative Coupling Reactions.

Transition-metal-catalyzed cross-coupling reactions are widely used in both academia and industry for the construction of carbon-carbon and carbon-heteroatom bonds. The vast majority of cross-coupling reactions utilize aryl (pseudo)halides as the electrophilic coupling partner. Carboxylic acid derivatives (RC(O)X) represent a complementary class of electrophiles that can engage in decarbonylative couplings to produce analogous products. This decarbonylative approach offers the advantage that RC(O)X are abundant and inexpensive. In addition, decarbonylative coupling enables both intramolecular (between R and X of the carboxylic acid derivative) as well as intermolecular bond-forming reactions (in which an exogeneous nucleophile is coupled with the R group derived from RC(O)X). In these intermolecular reactions, the X-substituent on the carboxylic acid can be tuned to facilitate both oxidative addition and transmetalation, thus eliminating the need for an exogeneous base. This Account details our group's development of a diverse variety of base-free decarbonylative coupling reactions catalyzed by group 10 metals. Furthermore, it highlights how catalyst design can be guided by stoichiometric organometallic studies of these systems.Our early studies focused on intramolecular decarbonylative couplings that transform RC(O)X to the corresponding R-X with extrusion of CO. We first identified Pd and Ni monodentate phosphine catalysts that convert aryl thioesters (ArC(O)SR) to the corresponding thioethers (ArSR). We next expanded this reactivity to fluoroalkyl thioesters, using readily available fluoroalkyl carboxylic acids as the fluoroalkyl (RF) source. A Ni-phosphinoferrocene catalyst proved optimal, and the large bite angle bidentate ligand was necessary to promote the challenging RF-S bond-forming reductive elimination step.We next pursued intramolecular decarbonylative couplings of aroyl halides. Palladium-based catalysts bearing dialkylbiaryl ligands (e.g., BrettPhos) were identified as optimal for converting aroyl chlorides (ArC(O)Cl) to aryl chlorides (ArCl). These ligands were selected based on their ability to facilitate the key C-Cl bond-forming reductive elimination step of the catalytic cycle. In contrast, all attempts to convert aroyl fluorides [ArC(O)F)] to aryl fluorides (ArF) were unsuccessful with either Pd- or Ni-based catalysts. Organometallic studies of the Ni-system show that C(O)-F oxidative addition and CO deinsertion proceed smoothly, but the resulting nickel(II) aryl fluoride intermediate fails to undergo C-F bond-forming reductive elimination.In contrast to its inertness to reductive elimination, this nickel(II) aryl fluoride proved highly reactive toward transmetalation. The fluoride ligand serves as an internal base, such that no additional base is required. We leveraged this "transmetalation active" intermediate to achieve base-free Ni-catalyzed intermolecular decarbonylative coupling reactions between aroyl fluorides and boron reagents to access both biaryl and aryl-boronate ester products. By tuning the electrophile, transmetalating reagent, and catalyst, this same approach also proved applicable to base-free intermolecular decarbonylative fluoroalkylation (between difluoromethylacetyl fluoride and arylboronate esters) and aryl amination (between phenol esters and silyl amines).Moving forward, a key goal is to identify catalyst systems that enable more challenging bond constructions via this manifold. In addition, CO inhibition remains a major issue leading to the requirement for high temperatures and high catalyst loadings. Identifying catalysts that are resistant to CO binding and/or approaches to remove CO under mild conditions will be critical for making these reactions more practical and scalable.

Catalytic Isopropanol Dehydration as a Model Reaction for Bio‐Oil Conversion into Light Olefins

AbstractCatalytic dehydration of isopropanol was studied as a model reaction for the conversion of bio‐oil into light olefins. γ‐Alumina synthesized in the laboratory and commercial ultrastable Y (USY) zeolite were used as catalysts. The catalytic activity and the effects of temperature, N2 flow, and catalyst loading were investigated. The highest conversions of isopropanol were achieved by employing USY zeolite. The model reaction tests also showed that a higher temperature favors a rise in the conversion of isopropanol. The increase in nitrogen flow allows better desorption of water molecules that possibly inhibit the reaction, thus increasing conversion. A higher catalyst loading also promoted a higher conversion of isopropanol due to the number of acidic sites available.

A chiral route to the synthesis of (2S,3aR,7aS)-tert-butyl hexahydro-2,5-methanopyrrolo[3,2-c]pyridine-1(4H)-carboxylate, an intermediate for nicotinic acetylcholine receptors agonists

A synthesis of (2S,3aR,7aS)-tert-butyl hexahydro-2,5-methanopyrrolo[3,2-c]pyridine-1(4H)-carboxylate (1A), a key intermediate for tricyclic compounds found as potent α7 nicotinic acetylcholine receptor ligands, following a novel chiral route is described here. The new chiral route circumvented two major challenges in the earlier route by avoiding high catalyst loading of pyrophoric Pd/C and reduced reaction time for the hydrogenation. The current methodology starts with a chirally defined intermediate which gives a strategic advantage over the previous scheme by being more convergent. Some of these improvements are discussed in detail in the current work.

Approaches on Improving Electroreduction of Carbon Monoxide to Acetate in Flow Electrolyzer

Acetic acid (CH3COOH) is an important industrial chemical that is widely used in the generation of various products including medicals, food, solvent, synthetic fibers and fabrics. Although most acetic acid production today relies on the carbonylation process of methanol1, electrochemical synthesis method is a promising direction owing to its uniqueness in ambient conditions, utilization of renewable energy, and compatibility with bioengineering2. Cupper has the capability to electrochemically reduce CO2 to various C2 products but with low selectivity. The critical steps for acetate molecule generation from CO2/CO are the CO-dimerization and the nucleophilic attack of hydroxide ion on a ketene intermediate3, in which acetate production could be enhanced by electroreducing CO in alkaline electrolyte as compared to CO2 electroreduction in pH neutral solution. Meanwhile, the use of flow electrolyzer further improved the gas transport process by employing gas diffusion electrode, boosting the current and yield rate of products to industrial level. However, electrochemical reduction of CO to acetate on Cu-based electrocatalysts still suffers from low faradaic efficiency (<50%).4 In this talk, we will present our recent work on CO electroreduction to acetate by commercial Cu catalyst in flow electrolyzer. Parameters in terms of electrolyte molarity, catalyst loading, catalyst deposition method, and ionomer were manipulated to maximize the acetate production. Acetate was favored in high pH electrolyte by facilitating the nucleophilic attack of hydroxide ion process and suppressing competing proton transfer process towards ethylene and ethanol. Catalyst loading on gas diffusion electrode had great influence on the products selectivity, where low catalyst loading leans to ethylene generation, intermediate catalyst loading is selective to produce acetate, and high catalyst loading improves alcohol yield. A record 68% faradaic efficiency of acetate from CO with partial current density of 102 mA/cm2 was reached. Reference A. Dimian and A. Kiss, Chem. Eng. Res. Des., 159 (2020).S. Guo, T. Asset, and P. Atanassov, ACS Catal., 5172–5188 (2021) https://pubs.acs.org/doi/abs/10.1021/acscatal.0c04862.M. Jouny et al., Nat. Chem., 11, 846–851 (2019) https://doi.org/10.1038/s41557-019-0312-z.W. Luc et al., Nat. Catal., 2, 423–430 (2019) https://doi.org/10.1038/s41929-019-0269-8. Figure 1

Optimising ex-situ catalytic fast pyrolysis of pine wood at pilot scale: Impacts on the energy content, chemical composition and stability of the liquid fuel product

A central composite design was used to optimise the yield and higher heating value (HHV) of the liquid fuel produced through ex-situ catalytic fast pyrolysis of pine wood. The variables were the temperature and loading of H-ZSM-5 zeolite catalyst. GC/MS, 1H NMR and stability tests were undertaken to compare the fuel properties of organic phases with similar HHVs, generated from catalytic treatments at low (≤ 370 °C) and high (≥ 470 °C) temperatures. When targeting an HHV of 32 MJ/kg, higher yields were obtained at low temperature and high catalyst loading, despite higher coke yield. Treatment at low temperature preserved more alkyl groups and made the fuel less aromatic (−13 % of aromatic hydrogen and lower content of Crich hydrocarbons). Undesirable catalytic cracking of alkyl groups at higher temperature was evidenced by a 60 % increase in the production of hydrocarbon gases. Despite a higher oxygen content, the fuel produced at low temperature was also found to be more stable.

SiO2‐Supported Ni(II) and Fe(II) Catalysts Bearing Sodium‐Sulfonate Group for Olefin Polymerization†

Comprehensive SummaryHeterogeneous catalysts have been dominant for industrial polyolefin production, offering many distinct advantages, such as controlling the morphology of the polymer and preventing reactor fouling. In this contribution, we designed several types of imine ligands bearing sodium‐sulfonate ionic groups and the corresponding nickel/iron catalysts. These catalysts could be immobilized on SiO2 with strong affinity and high catalyst loadings. The SiO2‐supported catalysts behaved better than their homogeneous counterparts during ethylene polymerization with extremely high activity (2.6 × 104 kg·mol−1·h−1) and high thermal stability. In addition, the supported nickel catalysts generated free‐flowing polyethylene with high molecular weight (Mn up to 2.65 × 103 kg·mol–1) and excellent morphology control, indicating no reactor fouling due to the leaching of catalyst. Moreover, for copolymerization, immobilized nickel catalysts showed a higher tolerance of polar monomers, and the efficient copolymerization of ethylene with undecylenic acid was achieved with high activity (450 kg·mol−1·h−1) and a high incorporation ratio (up to 12.3%).

Pd-NHC complex catalyzed C-H bond activation reactions of caffeine and 2-isobuthylthiazole

A series of new Pd-NHC complexes were synthesized, characterized, and utilized as catalysts on 8-(hetero)arylation of xanthines and C-5 (hetero)arylation of 2-isobuthylthiazole. All the synthesized derivatives were characterized by NMR, Q-TOF-LC/MS, FTIR, and X-ray (for 4a, 5a, and 5b) analysis. In addition, DFT calculations and computational NBO studies for Pd-NHC complexes were examined, and HOMO and LUMO energy levels and electron density of each Pd-NHC complex were defined. 4a-c and 5a-b complexes showed good catalytic activity in C-H bond activation reactions. DFT studies have also been conducted to examine the reaction mechanism following the CMD pathway. Complex 5a was chosen as a representative catalyst for the reaction of unsubstituted phenyl with caffeine and 2-isobuthylthiazole. Although the ΔE values of the complexes are so close, slight difference in the catalytic activity were observed for 4a-c and 5a-b. Since this low ΔE value facilitates the oxidative addition reaction of (hetero)aryl bromides, thanks to this catalytic system, new 8-(hetero)aryl xanthines and 5-(hetero)aryl thiazole derivatives could be synthesized with high yields and low catalyst loading.