The synthesis of value-added aromatic products, such as para-ethyl-toluene (PetT), from the greenhouse gas carbon dioxide (CO2) and renewable hydrogen (H2) is greatly desired. However, considerable challenges arise due to complex kinetics and difficulties in arranging multiple active components. Herein, we present a strategy for the selective synthesis of PetT via CO2 hydrogenation in the presence of ethylbenzene via tandem reactions over a composite catalyst comprising Zn-Zr binary oxide and a modified crystal-stacking HZSM-5 zeolite, achieving over 70% PetT selectivity in the ethyl-toluene (ET) isomers (∼80% in the C5+ hydrocarbons). State-of-the-art (quasi) in situ characterizations and corresponding theoretical calculations confirmed the designed reaction route involving stepwise activation of CO2 to methoxy species and enhanced aromatic cycles for the formation of C–C bonds. And precisely controlled transfer and transformation of intermediate methoxy species contribute to the promoted performance in the selective synthesis of PetT.

The synthesis of ethanol (EtOH) via hydrogenation of dimethyl oxalate (DMO) from syngas has gained wide attention, but its practical application is still limited by the poor selectivity on conventional Cu-based catalysts. This work developed an efficient Fe2C catalyst confined in the ordered mesoporous carbon (Fe/CMK-3) for the hydrogenation of DMO to EtOH. The formation of epsilon-carbide phase was favored by moderate carbonization process via stepwise methanol dissociation in a confined redox microenvironment. The lower energy barriers of the epsilon-carbide phase for C=O activation enhanced the intrinsic activity of Fe/CMK-3 in the deep hydrogenation of MA to EtOH, which was the rate-determining step of DMO hydrogenation. In addition, the confined effect of ordered mesoporous carbon allowed a high dispersion of the iron carbonates, which further boosted the EtOH production. On this catalyst, a high EtOH yield of 97.6%, an unprecedent space time yield of 1004 gEtOH kgcat(-1) h(-1), and a durability of 120 h were successfully achieved, which could provide an alternative route for the industrial production of ethanol from syngas conversion.

Designing effective catalysts using non-noble metals for bio-oil hydrodeoxygenation (HDO) into liquid fuels is greatly sought after, yet it remains a great challenge. Contrary to the prevailing belief that monometallic nickel lacked activity in the HDO of oxygen-containing compounds, this study demonstrates a remarkable catalytic performance over monometallic Ni catalyst. Herein, a Ni/SiO2 catalyst having both nickel phyllosilicate and Ni0 was synthesized by the ammonia evaporation (AE) method. The Ni-PS-400 catalyst reduced at 400 degree celsius achieves a significant high activity and yields 97 % cyclohexane at a low reaction temperature of 190 degree celsius, surpassing both Ni-IMP-400 prepared by impregnation method and most of the reported other non-noble metal catalysts which are generally used at high temperature of above 240 degree celsius. It was found that the reduction temperature of Ni-PS-X influences the catalytic activity, as more dispersed Ni nanoparticles and acidic sites can be produced on the surface of the support at an appropriate temperature. The outstanding catalytic performance can be ascribed to the collaborative effect of well-scattered Ni nanoparticles and the significant presence of Lewis acidic sites, which result from coordinatively unsaturated Ni2+ sites situated within the remaining nickel phyllosilicate.

The synthesis of valuable aromatics via CO2 transformation, especially para-xylene (PX), is of paramount significance but still remains greatly challenging due to the low efficiency and poor selectivity. The present work utilized a composite catalyst based on ZnZrOx with a modified H-ZSM-5 exhibiting nano-prism stacking to realize the selective synthesis of PX. Methoxy species generated from CO2-derived formate produced as an intermediate over the ZnZrOx were readily incorporated into the xylene products for effective alkylation, contributed to an enhanced aromatics-based cycle that provided a selectivity for xylenes among all C5+ hydrocarbons of 91.1 %. The lengthened straight channels in the H-ZSM-5 along the b-axis, derived from the crystal stacking pattern, increased differences in the diffusion properties of the xylene isomers, and thereby steering the movement of molecules toward a product shape-selective pathway, leading to 90.1 % selectivity for PX among all xylenes, and provided exceptional CO2 utilization efficiency of similar to 60 %.

Selective synthesis of specific value-added aromatics from CO2 hydrogenation is of paramount interest for mitigating energy and climate problems caused by CO2 emission. Herein, we report a highly active composite catalyst of ZnZrO and HZSM-5 (ZZO/Z5-SG) for xylene synthesis from CO2 hydrogenation via a coupling reaction in the presence of toluene, achieving a xylene selectivity of 86.5 % with CO2 conversion of 10.5 %. A remarkably high space time yield of xylene could reach 215 mg g(cat)(-1) h(-1), surpassing most reported catalysts for CO2 hydrogenation. The enhanced performance of ZZO/Z5-SG could be due to high dispersion and abundant oxygen vacancies of the ZZO component for CO2 adsorption, more feasible hydrogen activation and transfer due to the close interaction between the two components, and enhanced stability of the formate intermediate. The consumption of methoxy and methanol from the deep hydrogenation of formate by introduced toluene also propels an oriented conversion of CO2.

The urgent need for efficiency improvement in the oxide-zeolite bifunctional syngas-to-hydrocarbon catalysis necessitates in-depth mechanistic insights into this reaction, especially for the initial syn- gas conversion over the oxide component, which remains poor. Herein, we comprehensively investigated syngas conversion over a representative ZnAl2O4 spinel oxide with state-of-the-art solid- state NMR technologies. Notably, specific surface dual active sites for syngas activation with-AlIV-OH center dot center dot center dot ZnIII- structure were unam- biguously identified. More importantly, the dynamic evolution of the reaction intermediates and active sites during the reaction pro- cess was elaborated at atomic level by a series of double resonance and multi-dimensional correlation NMR experiments. In combina- tion with in situ spectroscopic characterizations, we revealed the full cycle of the formate-methoxy-based pathway for the syngas- to-methanol conversion via synergistic interplay of the dual active sites. The in-depth atomic-level understanding of the catalytic mechanism will be beneficial to further rational design of high- performance catalysts for syngas conversion.

The emerging oxide–zeolite bifunctional catalysis for direct syngas conversion has drawn extensive interest, both academically and industrially, with further exploration urging a clear mechanistic understanding of this complex catalytic network. Herein, using a specially designed quasi-in situ, solid-state nuclear magnetic resonance-gas chromatography/gas chromatography-mass spectrometry analysis strategy, this reaction is fully monitored from the very early induction period to steady-state conversion under high-pressure flow-reaction conditions, using ZnAlO x /H-ZSM-5 composites as model catalysts. We identify abundant critical and/or transient intermediates in dynamic evolution, including carboxylates, alkoxyls, acid-bounded methyl-cyclopentenones and methyl-cyclopentenyl carbocations, providing direct evidence of vigorous regulation by unique, oxygenate-based pathways of the reaction network. This proposed mechanism overturns the general cognition of oxide–zeolite reactions as simple tandem catalysis, and highlights the many roles (both positive and negative) of CO and H 2 molecules via oxygenate-based routes, thus dictating the final product. The current characterization technology and its mechanistic understanding would benefit further exploration in bifunctional catalysis.

Surface metal hydrides (M-H) are ubiquitous in heterogeneous catalytic reactions, while the detailed characterizations are frequently hindered by their high reactivity/low concentration, and the complicated surface structures of the host solids, especially in terms of practical solid catalysts. Herein, combining instant quenching capture and advanced solid-state NMR methodology, we report the first direct and unambiguous NMR evidence on the highly reactive surface gallium hydrides (Ga-H) over a practical Ga2O3 catalyst during direct H2 activation. The spectroscopic effects of 69Ga and 71Ga isotopes on the 1H NMR signal are clearly differentiated and clarified, allowing a concrete discrimination of the Ga-H signal from the hydroxyl crowd. Accompanied with quantitative and two-dimensional NMR spectroscopical methods, as well as density functional theory calculations, information on the site specification, structural configuration, and formation mechanism of the Ga-H species has been revealed, along with the H2 dissociation mechanism. More importantly, the successful spectroscopic identification and isolation of the surface Ga-H allow us to clearly reveal the critical but ubiquitous intermediate role of this species in catalytic reactions, such as propane dehydrogenation and CO2 hydrogenation reactions. The analytic approach presented in this work can be extended to other M-H analysis, and the insights will benefit the design of more efficient Ga-based catalysts.

Hydroxyl groups are among the major active surface sites over metal oxides. However, their spectroscopic characterizations have been challenging due to limited resolutions, especially on hydroxyl-rich surfaces where strong hydroxyl networks are present. Here, using nanostructured In2O3 as an example, we show significantly enhanced discrimination of the surface hydroxyl groups, owing to the high-resolution 1H NMR spectra performed at a high magnetic field (18.8 T) and a fast magic angle spinning (MAS) of up to 60 kHz. A total of nine kinds of hydroxyl groups were distinguished and their assignments (μ1, μ2, and μ3) were further identified with the assistance of 17O NMR. The spatial distribution of these hydroxyl groups was further explored via two-dimensional (2D) 1H-1H homonuclear correlation experiments with which the complex surface hydroxyl network was unraveled at the atomic level. Moreover, the quantitative analysis of these hydroxyl groups with such high resolution enables further investigations into the physicochemical property and catalytic performance characterizations (in CO2 reduction) of these hydroxyl groups. This work provides insightful understanding on the surface structure/property of the In2O3 nanoparticles and, importantly, may prompt general applications of high-field ultrafast MAS NMR techniques in the study of hydroxyl-rich surfaces on other metal oxide materials.

A phyllosilicate-derived NiFe/SiO2 catalyst (NiFe/SiO2-AE) was successfully prepared by the ammonia evaporation method and applied in the hydrodeoxygenation of phenol to cyclohexane. Another two catalysts were also prepared for a comparison by impregnation (NiFe/SiO2-IM) and deposition-precipitation (NiFe/SiO2-DP) methods, respectively. It was found that Ni-Fe alloy, the active sites for the hydrogenolysis of C-O bond, can be obtained by the reduction of NiFe2O4 (IM) or phyllosilicate (DP and AE) by H-2. The AE strategy can generate more phyllosilicate structure, which improves the dispersion of both Ni-Fe alloy and metallic Ni sites and allows the formation of more interface between these two kinds of sites as well. Therefore, the NiFe/SiO2-AE exhibits a significantly high catalytic performance in the HDO of phenol to cyclohexane. Moreover, the turnover frequency of Ni-Fe alloy sites over NiFe/SiO2-AE catalysts is much higher than those of other two catalysts. It is suggested that the enhanced synergy between the two kinds of active sites in the adsorption of C-O groups and hydrogen molecules ensures the superior intrinsic activity in HDO process.

To achieve high selectivity of styrene from toluene and methanol, a new strategy, the coupling of methanol dehydrogenation and side-chain alkylation of toluene by ternary composite catalyst combining methanol dehydrogenation, B/SiO2 and CsX components, is proposed. The methanol dehydrogenation component could promote the in-situ formation of formaldehyde (HCHO) intermediate, transferring to B/SiO2 and CsX components. The formation of HCHO over dehydrogenation component is driven by the side-chain alkylation reaction over CsX-B/SiO2 during the coupling reaction. In addition, B/SiO2 is beneficial to stabilize HCHO. When CuO/SiO2 is applied as the dehydrogenation component, the styrene and ethylbenzene yield reaches 31.0 % at a methanol conversion of 60.1 % with the styrene/ethylbenzene molar ratio in products of 3.1 over CsX-CuO/SiO2-B/SiO2. The effective method to prepare a ternary composite catalyst provide helpful guideline for developing a more efficient CsX-based catalyst for conversion of toluene with methanol into styrene in the further.

A method and key factors for preparing high performance catalysts for side-chain alkylation of toluene with methanol were developed and proposed.

A novel interzeolite transformation strategy using internally confined organic structure directing agents (OSDAs), called the "OSDA-confined" strategy, is proposed for highly crystalline nanosized high-silica ZSM-5 zeolite synthesis, by which high yield and fast synthesis of ZSM-5 is achieved using BEA zeolite as a raw material. The transformation process was investigated by XRD, SEM, ICP, FTIR and UV Raman spectroscopy, which revealed that the decomposition of a parent zeolite and the crystallization process of products were well modulated by the confined OSDA. The transformation process could be divided into three stages consisting of raw material deconstruction, small size product formation and product growth. The strong etching power of NaOH contributes to the fast decomposition of BEA zeolites. In addition, tetrapropylammonium hydroxide (TPAOH) as an OSDA was confined in the parent zeolite instead of being added into the mother liquid, achieving a high local concentration of TPAOH, which could reduce the decomposition rate of the parent BEA zeolite and promote the efficient organization of the building units generated by the decomposition of the BEA zeolite. Thereof, a high yield was achieved by the synergistic effect of NaOH and occluded TPAOH. During the interzeolite transformation process, the six-membered rings (6Rs), five-membered rings (5Rs) and four-membered rings (4Rs) in the BEA zeolite framework were disassembled and combined with the help of 5Rs to produce the ZSM-5 zeolite structure. Moreover, due to the nanoscale and large surface area, the obtained ZSM-5 zeolite catalyst showed extremely high catalytic activity in the self-etherification reaction of benzyl alcohol (BA) to dibenzyl ether (DE). This study provides insights into the interzeolite transformation process, which would be helpful for achieving size control and high-efficiency synthesis.

Hierarchical TS-1 (PTS-1) with intracrystalline mesopores have been synthesized through post-treatment with tetrapropyl ammonium hydroxide (TPAOH). The changes in physical and chemical properties of PTS-1 were studied in detail. The results showed that abundant mesopores were introduced via TPAOH treatment. Moreover, more silanol groups were generated, which enhanced the hydrophilicity of PTS-1. The hierarchical TS-1 with abundant mesopores showed higher catalytic activity than microporous TS-1 in the direct hydroxylation of toluene. In addition to powerfully enhanced the mesoporosity, the hydrophilicity of PTS-1 was also enhanced. The enhancement of hydrophilicity led to the adsorption capacity of toluene reduced, thus reducing the catalytic activity of PTS-1. The highest conversion of toluene and the yield of cresol could be reached 69.5 % and 67.2 %, respectively over the optimal catalyst and the regenerated catalyst exhibited excellent reusability. These findings provide a facile method to construct high active TS-1 catalysts for the direct hydroxylation of toluene.

The effect of the introduced base sites in CsX with alkali oxide modification towards side-chain alkylation of toluene with methanol was systematically investigated in the present work. A series of alkali oxide modified CsX with a base properties (base strength and amount) gradient were prepared by impregnating CsX with alkali metal hydroxide. Here, CsX with different base strengths were selected as the parent zeolite, which is favorable to clarify the different types of base site in the modified CsX. The base properties of the samples were elucidated based on the CO2-TPD results as well as with characterization by XPS and FT-IR of adsorbed CO2. It was revealed that the base strength of the oxygen atoms with negative charge (O δ-) in the zeolite framework can be strengthened by the electron donating function of the alkali oxides in the supercage of CsX. Detailed analysis of the correlation between the reaction behaviors of side-chain alkylation reaction and the base properties of the indicated catalysts was carried out. It was found that the dehydrogenation of methanol to formaldehyde step was promoted by the increasing base properties of O δ- in the CsX framework and that was the main reason for the promotion of the whole side-chain alkylation reaction. However, it was also found that the stronger base properties of the alkali oxide modified CsX would enhance the formation of active hydrogen atoms, which aggravated the unwanted styrene conversion to ethylbenzene.

An integrated catalyst that contains Fe5C2 and CuZnO-SiO2 with a dual-bed configuration was designed for the preferential synthesis of ethanol via dimethyl oxalate hydrogenation. The cooperation of the two catalyst components remarkably inhibited the formation of various byproducts, resulting in a significantly high ethanol yield of about 98%.

A new strategy, the coupling of methanol dehydrogenation and side-chain alkylation of toluene, to realize highly effective conversion of methanol and toluene into styrene and ethylbenzene was proposed. A series of composite catalysts were designed by combining CsX with numerous catalysts reported to be effective for methanol dehydrogenation to formaldehyde. The studies of side-chain alkylation of toluene with methanol over these composite catalysts indicated that the introduction of methanol dehydrogenation components could universally improve the yield of styrene and ethylbenzene in side-chain alkylation of toluene with methanol. And the introduction of some methanol dehydrogenation components, i.e. sodium borate (Na2B4O7) and CuO/SiO2, could even double the yield of styrene and ethylbenzene. Furthermore, the influence of the mass ratio of different components and the spatial arrangement of different active sites on composite catalysts was investigated in detail.

The catalytic hydrodeoxygenation (HDO) of lignin-derived phenolic compounds is a critical step in the upgrading of bio-oil. Here, bimetallic Ni-Fe nanoparticles supported on mesoporous carbon spheres (MCSs) were fabricated and applied in HDO of phenol. In comparison with monometallic Ni and Fe catalysts, the bimetallic Ni-Fe catalyst exhibited better performance for phenol HDO due to the formation of Ni-Fe alloy phase identified by X-ray powder diffraction (XRD) and Mossbauer spectroscopy techniques. Among several explored ratios, the catalysts with Ni/Fe ratio of 3/1 presented the highest cyclohexane yield. The reaction occurred in two consecutive steps: the hydrogenation of phenol to cyclohexanol and the further hydrogenolysis of cyclohexanol to cyclohexane. Kinetic studies showed that the hydrogenolysis of cyclohexanol controlled the overall reaction rate of phenol HDO due to the lower reaction rate of this step. Indeed, the turnover frequency (TOF) values of cyclohexanol normalized by surface metallic Ni sites exhibited a linear correlation with Ni-Fe alloy sites. The alloying of iron in the bimetallic Ni-Fe catalysts significantly enhanced the adsorption strength of cyclohexanol, which is the reason of the high activity of the Ni-Fe alloy particles. Thus, Fe-containing sites adsorb the hydroxyl species while Ni sites perform the H-2 activation, their synergistic effect plays a key role in phenol HDO process.

The crucial step for styrene production and the formation paths for the main side-products in the side-chain alkylation of toluene with methanol over CsX were unveiled.

tert-Butylation of naphthalene is a potential technology to produce 2,6-di-tert-butylnaphthalene (2,6-DTBN), which is a valuable raw material for the synthesis of polyethylene naphthalate (PEN). Alkaline, acid and combined alkaline-acid treatments were adopted to regulate the porosity and acidity of Al-rich HMOR zeolite. The structure, porosity and acidity of the catalysts were well characterized and the catalytic performance in the tertbutylation of naphthalene was extensively investigated. The strong acid sites were verified as the intrinsic active sites for naphthalene alkylation for the first time. Characterization results indicated that alkaline treatment could extract silicon from the framework and intra-crystalline mesopores with diameters of 3-30 nm were successfully generated in Al-rich HMOR by one-step alkaline treatment. The introduced mesopores could enhance the mass diffusion of molecules as well as the coke-resistance, despite that the high acid density in the internal surface would lead to fast coke deposition. On the other hand, the acid treatment could remove the aluminium efficiently, leading to significantly decreased strong acid sites located at the micropores and pore entrances, which reduced coke deposition in the channels and pore entrances and brought about sharp increase in the conversion rate of naphthalene per strong acid site. Thus, higher naphthalene conversion and di-tert-butyl naphthalene (DTBN) selectivity were obtained over all the post-treated samples. Besides, the high selectivity for 2,6-DTBN (2,6-/2,7-DTBN > 28.0) remained. More importantly, combined alkaline and acid treatment had synergistic effects on the improvement of the initial activity as well as the catalytic stability due to the optimized acidity and porosity.