Acid Sites In Zeolites Research Articles

Acid Site Density as a Kinetic Descriptor of Catalytic Reactions over Zeolites

A mathematical framework for the quantitative description of site density dependence of catalytic data (activity and selectivity) was developed considering that changes in the electrostatic contribution to the Gibbs energy of an elementary reaction on the acid sites in zeolites depend on the proximity of these sites. For the two-step sequence with the most abundant surface intermediate, an expression for turnover frequency explicitly containing the acid site density was derived. The treatment was extended to linear sequences of elementary reaction and analysis of the acid site density on selectivity in parallel and consecutive reactions, allowing to quantitatively relate the ratio between products for such reactions. Experimental data on Prins condensation of isopulegol with acetone and transformations of syngas over mesoporous H-ZSM-5 supported cobalt nanoparticles to a mixture of iso- and normal hydrocarbons were used as a show case.

Acidity regulation for improved activity of Mo/HZSM-5 catalyst in methane dehydroaromatization

The Mo/HZSM-5 is a widely studied bifunctional methane dehydroaromatization (MDA) catalyst, and the acid site of zeolite is essential to the reaction process. In this study, the relationship between acid site control and MDA reaction performance is investigated. The Brønsted/Lewis acid sites have been toned by introducing promoters to the ZSM-5 zeolite. It shows that proper strong Brønsted acid sites are conducive to aromatic formation, while excessive Brønsted acid sites will lead to serious coke deposition. Thus, the MDA catalytic stability is further improved by passivation of partial Brønsted acid sites of Mo/HZSM-5 via coating Silicalite-1 on the catalyst surface. The optimized catalyst shows 95 % aromatic selectivity at initial with only 0.06 h−1 deactivation rate constant. The surface of HZSM-5 is reconstructed after hydrothermal treatment and the surface aluminum content is reduced. Moreover, the Silicalite-1 layer is beneficial to Mo species dispersion for preventing its aggregation and stabilizing the Mo-C active sites.

DFT Study on the Stability and the Acid Strength of Brønsted Acid Sites in Zeolite β.

Acid sites are studied computationally for zeolite β. Different deprotonated and protonated models are used. The issue of difference in the stability of acid sites is addressed. Separate and paired acid sites are created, and their stability and acidity are estimated. The sites in the 6-membered rings have a favorable position; however, the study does not exclude the diversity of sites in other positions. The zeolite module and model chemistry have an influence on the computational results. The influence of the mutual arrangement of two acid sites in a single model is studied. Hydrogen bonding influences the stability and acidity in this case. Four and six acid sites are created that possess hydrogen bonding in the same model. The distance and mutual orientation of the sites affect their stability. Thus, the dipole-dipole interactions, structure deformations, and inductive effect all play their roles in the chemistry of the acid sites. Both thermodynamics and chemical kinetics of the zeolite can influence Al locations in zeolites, and their influence should be concerted according to the linear relation of the free energies.

Synergistic effect of Brønsted/Lewis acid in olefin aromatization during MTO over Zn modified H-SAPO-34 zeolite: A periodic DFT study

H-SAPO-34 modified with extra-framework Zn2+ cations improved the selectivity to ethene and ratio of ethene to propene in the early stage of the methanol-to-olefin (MTO) reaction. In order to reveal the promotion mechanism, density functional theory calculations were performed to study the aromatization of 3-methyl-1,3-pentadiene to m-xylene. On three Zn-modified H-SAPO-34, the methylation and dehydrogenation processes, which are the key reactions of olefin aromatization over undoped H-SAPO-34, were studied in detail. It is found that the methylation reaction is more likely to occur at Brønsted acid sites (BAS), and the spatial proximity of BAS and Lewis acid sites (LAS) in zeolite enhances the acidic strength of BAS, thereby improving the methylation activity. The dehydrogenation reaction occurring at the LAS provided by Zn2+ proceeds via the "carbenium" mechanism, with significantly reduced energy barriers and improved dehydrogenation activity. This dehydrogenation mechanism was further testified by the metadynamics (MetaD) simulations. The synergistic effect of Brønsted acid and Lewis acid enables Zn2+ modified H-SAPO-34 to have high olefin aromatization activity, which in turn regulates the selectivity of lower olefins. The present results well interpret the experimental observation that the ethene selectivity is improved at the initial stage of MTO.

Effect of ZSM-5 Particle Size and Framework Silica-to-Alumina Ratio on Hexane Aromatization

Parent ZSM-5 and Ga-modified ZSM-5 catalysts with different Si/Al ratios and particle sizes were prepared. The physicochemical properties of the prepared catalysts were investigated by performing X-ray powder diffraction analysis, BET surface area analysis, and NH<sub>3</sub>-TPD analysis. The performance of the aromatization reaction of the prepared catalysts was evaluated with 1-hexane as a model compound. The zeolite catalysts with a low SiO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub> ratio possessed better activity than those with a high SiO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub> ratio. Ga modification significantly improved the catalyst aromatization selectivity. Through aromatization, the acid sites of Ga-modified nano-sized zeolites promoted the selective conversion of produced olefin to aromatics by removing H-atoms. For the parent ZSM-5 and Ga-modified catalysts, the catalyst stability increased with an increase in the SiO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub> molar ratio. The nano-sized ZSM-5 catalyst with a high SiO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub> ratio exhibited better catalytic stability than the microscale ZSM-5, and the nano-sized catalyst with a low SiO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub> ratio showed very low stability.

Synergistic catalysis of Ru single-atoms and zeolite boosts high-efficiency hydrogen storage

Liquid organic hydrogen carriers (LOHCs) are promising hydrogen carriers that play an important role in the hydrogen economy. However, designing an efficient catalyst for realizing hydrogen storage with cost-effective and low-temperature is still a great challenge. Herein, we report a Ru single-atoms supported on *BEA zeolite catalyst (Ru(Na)/Beta), with the assistance of hydrogen spillover, which can remarkably enhance the hydrogenation of N-ethylcarbazole(NEC), N-propylcarbazole(NPC) and 2-methylindole (2-MID) at lower temperatures with lower Ru content (0.5 wt%). Notably, the obtained Ru(Na)/Beta catalyst exhibits excellent activity in the hydrogenation of NEC with the hydrogen uptake of 5.69 wt% and a conversion rate of > 99% within 1.5 h for the 6 MPa H2 at 100 °C, whereas the hydrogen uptake on traditional Ru/Al2O3 is only 2.97 wt% with the conversion rate of 67 % under the same conditions. It is found that highly dispersed Ru single-atoms boost hydrogen activation and the strong acid sites (Brønsted and Lewis) of zeolites promote the hydrogen spillover on the hydrogenation with N-heterocycles. Moreover, the synergistic effect of Ru single atoms and *BEA zeolite is crucial for accelerating the hydrogenation rate and lowering the activation energy (45.7 vs. 88.3 kJ/mol) compared with traditional Ru-based catalysts.

Promoting effect of alkali metal on the catalytic performance of hierarchical Pt/Beta in the aromatization of n-heptane

Previous research showed that hierarchical Beta zeolite supported Pt was an effective catalyst for the aromatization of alkanes and the modification with K could further enhance its catalytic performance; however, the intrinsic effect of alkali metal on the alkanes aromatization over Pt/Beta was still rather obscure. In this work, a series of hierarchical Pt/Beta-Me catalysts were prepared by modifying the Beta zeolite with different alkali metal nitrates (MeNO3, Me = Li, Na, K and Rb) through ion-exchange and used in the aromatization of n-heptane; the effect of alkali metal on the catalytic performance of Pt/Beta-Me was then systematically investigated. The results indicate that the alkali metals used to modify the Pt/Beta-Me catalysts can not only passivate the strong Brønsted acid sites of Beta zeolite, but also enhance the Pt dispersion and induce an electron-rich chemical environment for the supported Pt species. Accordingly, the modification with alkali metal can effectively suppress the cracking reactions and carbonaceous deposition and meanwhile promote the dehydroaromatization of alkanes, in favor of enhancing the catalytic stability and aromatization selectivity of Pt/Beta-Me. The extent of promoting effect of various alkali metals follows the order of Rb > K > Na > Li. In particular, the Pt/Beta-Rb catalyst exhibits excellent performance in the aromatization of n-heptane, with a much higher selectivity to aromatics (78.2%) and larger turnover number of aromatic products (Pt-based TON, 19.4 × 103) than the unmodified Pt/Beta-H one (27.7% and 4.8 × 103, respectively). These results help to clarify the role of alkali metal played in the catalysis of Pt/Beta-Me for n-heptane aromatization and pave the way for designing more efficient catalysts in the aromatization of alkanes.

Hydrogen-Bond-Assisted Adsorption of Nitric Oxide on Various Metal-Loaded ZSM-5 Zeolites.

Understanding the characteristics of nitric oxide (NO) adsorption on metal-loaded zeolites is a prerequisite for developing efficient catalysts for NO abatement reactions. In this study, we probed the effect of the hydrogen bond that exists between adsorbed NO and Brønsted acid sites (BAS) in various metal-loaded ZSM-5 zeolites (M-ZSM-5, wherein M = Fe, Co, Ni, Cu, Zn, Pd, Ag, and Au) by using density functional theory calculations. The presence of a hydrogen bond has altered the NO adsorption energies significantly; appreciable stabilization via hydrogen bonding is noted for NO complexes of Zn, Fe, and Co, and reasonable stabilization is obtained for Ni and Cu complexes, whereas an anomalous effect of a hydrogen bond is identified in Ag, Pd, and Au species. Moderate weakening of the N-O bond in all NO-adsorbed complexes primarily due to a hydrogen bond has been realized in terms of Mayer bond order and quantum theory of atoms in molecules topological analyses; N-O bond activation follows the order Ag < Pd < Au < Ni < Cu < Co < Fe < Zn. We obtained a good correlation between hydrogen bond distance and molecular electrostatic potential at the O atom (VO) of NO adsorbed on BAS-free M-ZSM-5; which suggests that VO can be considered as a key descriptor to infer the strength of a hydrogen bond between the adsorbed NO and M-ZSM-5 with BAS. Finally, the energy decomposition analysis in combination with natural orbitals for chemical valence has provided the qualitative aspects of electron back-donation from the metal to the antibonding molecular orbital of NO; this back-donation is quite impressive in hydrogen-bond-assisted NO adsorption. We expect that the findings of this study will open up the possibility of the design of BAS-containing metal-loaded zeolites for the catalytic mitigation of NO.

Regulating the distribution of acid sites in ZSM-11 zeolite with different halogen anions to enhance its catalytic performance in the conversion of methanol to olefins

Purposive regulation of the spatial location and distribution of acid sites in a zeolite catalyst, though still rather challenging, has proved to be an effective measure to enhance its performance in the conversion of methanol to olefins (MTO). Herein, a series of ZSM-11 zeolites were synthesized using different sodium halides (with tetrabutylammonium hydroxide (TBAOH) as the structure-directing agent); the effect of halogen anions (Cl-, Br- and I-) in the synthesis gel on the Al siting and thereon the spatial location and distribution of acid sites in the ZSM-11 zeolites as well as their relation to the catalytic performance in MTO was elaborately investigated. The results indicate that for the synthesis of high Si/Al ratio ZSM-11 zeolites (Si/Al > 60), the Cl- anions present in the synthesis gel can induce more Al atoms siting on the external surface of ZSM-11 crystals, thereby leading to a short catalytic lifetime in MTO due to the rapid coke deposition. In contrast, larger Br- or I- anions in the synthesis gel, owing to their stronger covalent interaction with the TBA+ cations, may moderate the formation of crystal silicate nuclei and lead to a uniform distribution of Al species in the inner straight channels, which can effectively suppress the surface coke deposition and inhibit the aromatic-based cycle for MTO. As a result, the high Si/Al ratio ZSM-11 zeolites obtained with Br- or I- in the synthesis gel exhibit much better catalytic stability in MTO and higher selectivity to propene and butene, in comparison with the ZSM-11 counterpart synthesized using Cl-. These results help to clarify the relation between the catalytic performance of ZSM-11 in MTO and the location of acid sites and thus bring forward a facile strategy to enhance the catalytic performance of zeolites through purposively regulating the spatial distribution of acid sites.

Maximizing noble metal utilization in solid catalysts by control of nanoparticle location

Maximizing the utilization of noble metals is crucial for applications such as catalysis. We found that the minimum loading of platinum for optimal performance in the hydroconversion of n-alkanes for industrially relevant bifunctional catalysts could be reduced by a factor of 10 or more through the rational arranging of functional sites at the nanoscale. Intentionally depositing traces of platinum nanoparticles on the alumina binder or the outer surface of zeolite crystals, instead of inside the zeolite crystals, enhanced isomer selectivity without compromising activity. Separation between platinum and zeolite acid sites preserved the metal and acid functions by limiting micropore blockage by metal clusters and enhancing access to metal sites. Reduced platinum nanoparticles were more active than platinum single atoms strongly bonded to the alumina binder.

Structure and Framework Association of Lewis Acid Sites in MOR Zeolite.

Zeolites, although key materials used in industrial processes, remain poorly understood on a molecular level despite their well-defined crystal lattices. In fact, obtaining a direct spectroscopic signatures and resolving the structure of Lewis acid sites (LAS) has remained a challenge. In this work, thanks to 1D and 2D 1H, 15N, and 27Al MAS NMR spectroscopy, carried out at different temperatures (from 298 down to 107 K), we were able to obtain the NMR spectroscopic signatures of LAS and Brønsted acid sites (BAS) in mordenite zeolite in the presence and the absence of adsorbed pyridine (Py). Combined with DFT modeling, this information enabled the structure of LAS to be revealed, namely (≡SiO)3Al sites interacting with pyridine, thus indicating that the corresponding base-free framework-associated sites are pseudo tricoordinated Al sites, namely tricoordinated Al sites interacting with an additional coordinated adjacent siloxane bridge. With this information in hand, we propose a molecular-level understanding on how the AlIV and AlVI framework and framework-associated sites evolve upon dehydration and exposure to Py into BAS and LAS, and their associated Py adducts. By measuring and analyzing the changes in quadrupolar coupling constants (CQ) that reflect electrical charge distribution around the nuclei, we further show that the lower CQ values observed at 298 K are due to residual dynamics that makes the electric field around aluminum nuclei more symmetric. Thus, NMR spectroscopic signatures of 27Al greatly vary with temperature; this information illustrates the importance of accounting for the temperature effect when confronting experimental and calculated CQ values of the corresponding aluminum sites in zeolites in order to obtain accurate structural assessment.

Mechanistic insights into the interaction between binders and Y-type zeolites in fluid catalytic cracking

Binders play essential roles in fluid catalytic cracking catalysts, and their interaction mechanism with zeolites remains to be explored. The effects of three binders on REUSY zeolite were investigated. The alumina sol most notably blocked the pore channels and destructed the framework of zeolites by removing the framework Al. The silica sol diffused into the silicon hydroxyl nests and form new Si-O tetrahedrons, which enhanced the structural stability and increased the number of Bronsted acid sites in zeolites, rendering the samples’ better hydrothermal stability and higher micro-reaction activity. The influence of the colloidal sol of pseudo boehmite on zeolites was between the two.

Modulating inherent lewis acidity at the intergrowth interface of mortise-tenon zeolite catalyst

The acid sites of zeolite are important local structures to control the products in the chemical conversion. However, it remains a great challenge to precisely design the structures of acid sites, since there are still lack the controllable methods to generate and identify them with a high resolution. Here, we use the lattice mismatch of the intergrown zeolite to enrich the inherent Lewis acid sites (LASs) at the interface of a mortise-tenon ZSM-5 catalyst (ZSM-5-MT) with a 90° intergrowth structure. ZSM-5-MT is formed by two perpendicular blocks that are atomically resolved by integrated differential phase contrast scanning transmission electron microscopy (iDPC-STEM). It can be revealed by various methods that novel framework-associated Al (AlFR) LASs are generated in ZSM-5-MT. Combining the iDPC-STEM results with other characterizations, we demonstrate that the partial missing of O atoms at interfaces results in the formation of inherent AlFR LASs in ZSM-5-MT. As a result, the ZSM-5-MT catalyst shows a higher selectivity of propylene and butene than the single-crystal ZSM-5 in the steady conversion of methanol. These results provide an efficient strategy to design the Lewis acidity in zeolite catalysts for tailored functions via interface engineering.

Excellent catalytic performance over hierarchical ZSM-48 zeolite: Cooperative effects of enhanced mesoporosity and highly-accessible acidity

Hydroisomerization has been considered as an effective and efficient route for production of transportation fuels and lubricants with superior cold-flow properties. In current work, n-hexadecane (n-C16) hydroisomerization was investigated over Pt catalysts supported on hierarchical ZSM-48, which was post-treated by multi-step procedures including alkaline-acid, acid-alkaline-acid, steaming-alkaline-acid, and fluorination-alkaline-acid leaching. This work was purposed to construct the secondary mesoporous network, enhance the accessible acid sites in hierarchical ZSM-48 zeolite, and investigate their cooperative effects on hydroisomerization performance. The results demonstrated that the microporosity and the crystallinity were preserved after the controllable leaching, coupled with more exposed accessible acidity and enhanced mesoporosity. High dispersion of Pt particles and quantitative metal-acid balance were unable to be the threats for the sequential acid-catalyzed reaction. The cooperative effects of enhanced mesoporosity and highly-accessible acidity accelerated the diffusion and promoted the proximity of metal sites and acid sites, thereby persuading the treated ZSM-48 samples to exhibit excellent activity and iso-selectivity. The i-C16 yield over Pt/ZSM-48(H) catalyst could reach around 86 wt% at conversion rates of 90 wt% with iso-selectivity of 96 wt%. However, the excessively accessible acid sites in Pt/ZSM-48(F) could induce further skeletal transformation and deteriorate the iso-selectivity, although the mesoporous structure was as well established.

Experiment and modeling of coke formation and catalyst deactivation in n-heptane catalytic cracking over HZSM-5 zeolites

Since paraffins catalytic cracking was of significant importance to light olefins and aromatics production, this work was intended to gain insights into the feature and model of coke formation and catalyst deactivation in n-heptane catalytic cracking over HZSM-5 zeolites. 18 tests of n-heptane catalytic cracking were designed and carried out over HZSM-5 zeolites in a wide range of operating conditions. A particular attention was paid to the measurement of the conversion, product distribution, coke content, and the porosity and acidity of the fresh and spent HZSM-5 zeolites. It was found that alkene and aromatic promoted coke formation, and it reduced the pore volume and acid site of HZSM-5 zeolites, tailoring its performance in n-heptane catalytic cracking. The specific relationship between HZSM-5 zeolites, n-heptane conversion, product distribution and coke formation was quantitively characterized by the exponential and linear function. Based on the reaction network, the coupled scheme of coke formation and catalyst deactivation were specified for n-heptane catalytic cracking. The dual-model was proposed for the process simulation of n-heptane catalytic cracking over HZSM-5 zeolites. It predicted not only the conversion and product distribution but also coke content with the acceptable errors.

One-pot, cascade conversion of cellulose to γ-valerolactone over a multifunctional Ru–Cu/zeolite-Y catalyst in supercritical methanol

A one-pot cascade conversion of cellulose to GVL was investigated over bimetallic Ru–Cu deposited on a zeolite Y (Ru–Cu/Z) catalyst. Under supercritical methanol conditions, high-yield (49.8%) cascade conversion of cellulose to GVL was achieved at 250 °C, with an initial H2 pressure of 3.0 MPa and reaction time of 5 h. The Ru–Cu/Z catalyst was synthesized using activated reductive deposition (ARD), which resulted in the selective deposition of Cu nanodomains on Ru nanoparticles, thereby facilitating the dissociative adsorption of H2. In addition, Lewis and Brønsted acid sites of Cu-doped zeolite Y effectively proceeded to cascade conversion reactions, including alcoholysis, isomerization, dehydration, and acetalization reactions, suppressing humin formation. The bimetallic Ru–Cu/Z catalyst was used in six consecutive runs, with a marginal loss of activity. The structure–performance relationships of the Ru–Cu/Z catalysts synthesized using ARD, incipient wet impregnation, and reduction deposition methods were compared.

On the Nature of Extra-Framework Aluminum Species and Improved Catalytic Properties in Steamed Zeolites.

Steamed zeolites exhibit improved catalytic properties for hydrocarbon activation (alkane cracking and dehydrogenation). The nature of this practically important phenomenon has remained a mystery for the last six decades and was suggested to be related to the increased strength of zeolitic Bronsted acid sites after dealumination. We now utilize state-of-the-art infrared spectroscopy measurements and prove that during steaming, aluminum oxide clusters evolve (due to hydrolysis of Al out of framework positions with the following clustering) in the zeolitic micropores with properties very similar to (nano) facets of hydroxylated transition alumina surfaces. The Bronsted acidity of the zeolite does not increase and the total number of Bronsted acid sites decreases during steaming. O5Al(VI)-OH surface sites of alumina clusters dehydroxylate at elevated temperatures to form penta-coordinate Al1O5 sites that are capable of initiating alkane cracking by breaking the first C-H bond very effectively with much lower barriers (at lower temperatures) than for protolytic C-H bond activation, with the following reaction steps catalyzed by nearby zeolitic Bronsted acid sites. This explains the underlying mechanism behind the improved alkane cracking and alkane dehydrogenation activity of steamed zeolites: heterolytic C-H bond breaking occurs on Al-O sites of aluminum oxide clusters confined in zeolitic pores. Our findings explain the origin of enhanced activity of steamed zeolites at the molecular level and provide the missing understanding of the nature of extra-framework Al species formed in steamed/dealuminated zeolites.

Enhancing the catalytic performance of H-ITQ-13 zeolite in the conversion of methanol to olefins through regulating the aluminum distribution in its framework

Herein, K+ was added in the synthesis gel to regulate the distribution of acid sites in the ITQ-13 zeolite and enhance its catalytic performance in the conversion of methanol to olefins (MTO). The results indicate that a proper content of K+ ions in the synthesis gel can not only expedite the crystallization of ITQ-13 zeolite, but also significantly decrease the proportion of paired Al and distribute more Al atoms in the 10-ring sinusoidal channel out from the intersection cavity. Accordingly, over the H-ITQ-13(0.3 K) zeolite prepared using the synthesis gel with a KCl/Al2O3 molar ratio of 0.3, the alkene cycle of MTO keeping to the dual cycle hydrocarbon pool (HCP) mechanism is preferably enhanced, whereas the hydride transfer and aromatization reactions are substantially suppressed. As a result, H-ITQ-13(0.3 K) exhibits much longer catalytic lifetime and higher selectivity to propene and butene, in comparison with the H-ITQ-13 counterpart obtained without adding K+.

Tuning Lewis acid sites in TS-1 zeolites for hydroxylation of anisole with hydrogen peroxide

One-step direct hydroxylation of aromatics is an atom-economic way for phenols production. Ti-containing MFI zeolite is considered to be one of the most potential catalysts for hydroxylation of aromatics to phenols under mild condition with aqueous H 2 O 2 as the oxidant. However, the products are often a mixture of mono- or multi-phenols. Designing TS-1 zeolite catalyst with high yield and selectivity to the target phenols remains a challenging task. Here TS-1 zeolites are prepared by direct hydrothermal and post-synthetic methods. Multiple spectroscopic characterizations show that the crystallinity and Ti-Lewis acid sites (Ti-LASs) distribution of TS-1 zeolite can be controlled by the synthetic approach. The structure-activity relationship of TS-1 zeolite is established in the catalytic hydroxylation of anisole, revealing that Ti-LASs concentration determines the conversion of anisole, while both the crystallinity and Ti-LASs distribution significantly influence the selectivity to the desired product para -hydroxyanisole. •The Ti-Lewis acid properties of TS-1 zeolites can be precisely modulated by the sample preparation. •The concentration of Ti-LASs in TS-1 determines the conversion of anisole hydroxylation. •Introducing Ti-LASs into the well-crystalized TS-1 channels facilitates the selective production of para-isomers in the hydroxylation of anisole. •This work provides insights into the understanding of the catalytic properties of TS-1 zeolites towards the selective hydroxylation of anisole to phenols.

Probing Acid Sites in MOR Zeolite Using Low-Temperature 13C Solid-State NMR Spectroscopy of Adsorbed Carbon Monoxide

Understanding the structure of Lewis and Brønsted acid sites in zeolites is a key step toward unraveling mechanisms of catalytic reactions, establishing molecular-level structure–activity relationships and thereby rational improvement of their performance. Acid sites are typically studied indirectly, using probe molecules, whose spectroscopic signatures are linked to the nature of specific sites. In this context, carbon monoxide and pyridine (Py) are the most frequently used probe molecules due to their sensitivity toward the nature and strength of surface acid sites. Although infrared and solid-state NMR spectroscopies of adsorbed Py are now widely used, the utilization of carbon monoxide to study surface sites has been mainly limited to infrared spectroscopy. Considering that NMR spectroscopy parameters, such as isotropic chemical shift (δiso) and chemical shift anisotropy (CSA), provide detailed structural information, we have explored the capabilities of low-temperature carbon-13 NMR spectroscopy of adsorbed 13CO on dehydrated mordenite. One-dimensional (1D) and two-dimensional (2D) 13C low-temperature magic-angle spinning NMR spectra show that carbon monoxide interacting with Lewis (LAS) and Brønsted (BAS) acid sites displays distinct 13C NMR signatures, in line with density functional theory (DFT) calculations. Furthermore, {1H}13C HETCOR NMR allows the observation of surface OH groups interacting with CO and points to the spatial proximity (within 1 nm) of BAS to both Si-OH and Al-OH groups, while LAS predominantly comprises the Al-OH group. These observations suggest the formation of defective aluminum sites with one and/or two OH groups bound to aluminum, upon calcination of a NH4-MOR with Si/Al = 6 at high temperature (580 °C). The NMR protocol discussed is perfectly suited to explore the surface sites of other solid materials.