Acid Sites Of Catalyst Research Articles

The Influence of Inserted Metal Ions on Acid Strength of OH Groups in Faujasite

The number and the strength of acid sites in catalysts have paramount importance on their efficiency. In zeolites chemistry, increased content of framework Al in zeolites gives a higher number of strong acid sites. Their strength can be a disadvantage in catalytic reactions (e.g., methanol to olefins conversion) due to undesired secondary reactions of coke formation. Here, the Faujasite type of zeolite with higher content of Al has been used for investigating the role of defects in structure and inserted (wet impregnation and thermal treatment) metal cations (Mg, Co, Ni, Zn) on the strength of OH acid sites. Desorption of deuterated acetonitrile, as a probe molecule, was used for OH groups acid strength measurements at different temperatures (150, 200, and 300 °C).

Rational Regulation of Reducibility and Acid Site on Mn-Fe-BTC to Achieve High Low-Temperature Catalytic Denitration Performance.

Selective catalytic reduction with ammonia is the mainstream technology of flue gas denitration (de-NOx). The reducibility and acid site are two important factors affecting the de-NOx performance, and effective regulation between them is the key to obtain a highly efficient de-NOx catalyst. Herein, a series of Mn-Fe-BTC with different ratios of Mn and Fe are synthesized, among which 2Mn-1Fe-BTC with 2:1 molar ratio of Mn and Fe has excellent low-temperature (LT) de-NOx performance (above 90% NO conversion between 60 and 270 °C) and good tolerance to H2O and SO2 poisoning (88% NO conversion at 150 °C with 100 ppm of SO2 and/or 6% H2O). It is revealed that the reducibility properties and acid sites of Mn-Fe-BTC can be flexibly tuned by the ratio of Mn and Fe. The difference in electronegativity between Fe and Mn leads to the redistribution of valence electrons, which enables the controllable reducibility of Mn-Fe-BTC. Furthermore, different amounts of Mn and Fe lead to different electron transport, which determines the type and number of acid sites. The synergistic effect of Mn and Fe endows Mn-Fe-BTC with enhanced surface molecular adsorption capacity and enables the catalyst to selectively chemisorb NH3 and NO at different active sites. This research provides guidance for the flexible regulation of reducibility and acid site of LT de-NOx catalyst.

Structure-property-performance relationship of transition metal doped WO3 mixed oxides for catalytic degradation of organic pollutants

Transition metal doped WO3 mixed oxides (named as W-M-O, M = Nb, Fe, Cr, Cu, Ti or Sn, respectively) with high structure stability were synthesized by modified sol-gel method using citric acid as organic crosslinking agent, and were evaluated for catalytic elimination of low-concentration toluene, monochlorobenzene and 1,2-dichloroethance with high toxicity and relatively stable molecule structure, as the typical examples for the pollutants of various volatile organic compounds (VOCs). Results of the structure-property-performance relationship research showed that mesoporous structure and nanocrystalline/amorphous state were formed, and binary metal components were dispersed into each other, which contributed to promoting the metal/metal electron interaction and adjusting the physicochemical properties of mixed metal oxides. The sequence of apparent catalytic activity for toluene degradation was: W–Nb–O＞W–Fe–O＞W–Cr–O, W–Cu–O＞W–Ti–O＞W–Sn–O＞WO3, and the sequence for monochlorobenzene degradation was: W–Nb–O＞W–Fe–O＞W–Cr–O, W–Ti–O＞W–Cu–O＞W–Sn–O＞WO3. There existed cooperative catalytic effect: mesopore and surface acid sites of catalysts facilitated adsorption, activation and breakage of the C-X bond, and then redox sites of catalysts promoted deep oxidation of a series of reaction intermediates to transform into CO2 and H2O. Especially, the optimized W–Nb–O catalyst deserved more attention, since it represented remarkable catalytic activity, selectivity and durability for three typical VOCs degradation along with good resistance to water vapor and corrosion of HCl.

Novel preparation method, catalytic performance and reaction mechanisms of PrxMn1−xOδ/3DOM ZSM-5 catalysts for the simultaneous removal of soot and NOx

Three dimensionally-ordered macroporous (3DOM) ZSM-5 zeolite catalysts with hierarchical pore structures have obvious advantages for the catalytic reaction systems containing reactants with different sizes. However, due to the stringent preparation conditions and confined crystallization space, the successful preparation of 3DOM ZSM-5 remains challenging. Herein, we report a novel method for the preparation of 3DOM ZSM-5 zeolite, termed the steam seed-assisted colloid crystal template (SSAC) method. The SSAC method avoids the growth of ZSM-5 crystals based on the confinement effect of the interstices of the polymethylmethacrylate (PMMA) template. The crystallization temperature of ZSM-5 is lower than the glass transition temperature of PMMA, which facilitates the formation of the 3DOM structure. Using 3DOM ZSM-5 as a support, a series of PrxMn1-xOδ/3DOM ZSM-5 catalysts were prepared via incipient wetness impregnation. These catalysts exhibited good catalytic performance for the simultaneous removal of soot and NOx, which can be attributed to the unique hierarchical pore structure, excellent redox properties, the sufficient active oxygen species and appropriate acid sites of overall catalysts. Among the synthesized catalysts, Pr0.2Mn0.8Oδ/3DOM ZSM-5 achieved the highest catalytic activity with a low soot combustion temperature of 417 °C and a wide temperature window of 128 °C-288 °C at 90% NO conversion. Finally, we proposed reaction mechanisms for the catalysts under different temperatures based on the in situ characterization results, kinetic measurements and DFT calculations.

Effect of inorganic salt on the removal of typical pollutants in wastewater by RuO2/TiO2 via catalytic wet air oxidation

The treatment of high-salinity and high-organic wastewater is a tough task, with the removal of organic matter and the separation of salts often mutually restricting. Catalytic wet air oxidation (CWAO) coupled desalination technology (membrane distillation (MD), membrane bioreactor (MBR), ultrafiltration (UF), nanofiltration (NF), etc.) provides an effective method to simultaneously degrade the high-salinity (via desalination) and high-organic matters (via CWAO) in wastewater. In this work, five kinds of RuO2/TiO2 catalysts with different calcination temperatures were prepared for CWAO of maleic acid wastewater with a theoretical chemical oxygen demand (COD) value of 20,000 mg L−1. RuO2/TiO2 series catalysts demonstrated prominent salt resistance, with more than 80% TOC removal rates in the CWAO system containing 5 wt% Na2SO4; while RuO2/TiO2-350 showed the best degradation performance in both non-salinity and Na2SO4-containing conditions. Multiple characterization techniques, such as XRD, BET, XPS, NH3-TPD and TEM etc., verified the physicochemical structure of RuO2/TiO2 catalysts, and their influence on the degradation of pollutants. The calcination temperature was found to have a direct impact on the specific surface area, pore volume, oxygen vacancies and acid sites of catalysts, which in turn affected the ultimate catalytic activity. Furthermore, we also investigated the performance of the RuO2/TiO2-350 catalyst for the treatment of acids, alcohols and aromatic compounds with the addition of NaCl or Na2SO4, proving its good universality and excellent salt resistance in saline wastewater. Meanwhile, the relationship between the structure of three types of organic compounds and the degradation effect in the CWAO system was also explored.

Counting the Acid Sites in a Commercial ZSM-5 Zeolite Catalyst.

This work investigates the acid sites in a commercial ZSM-5 zeolite catalyst by a combination of spectroscopic and physical methods. The Brønsted acid sites in such catalysts are associated with the aluminum substituted into the zeolite lattice, which may not be identical to the total aluminum content of the zeolite. Inelastic neutron scattering spectroscopy (INS) directly quantifies the concentrations of Brønsted acid protons, silanol groups, and hydroxyl groups associated with extra-framework aluminum species. The INS measurements show that ∼50% of the total aluminum content of this particular zeolite is extra framework, a conclusion supported by solid-state NMR and ammonia temperature-programmed desorption (TPD) measurements. Evidence for the presence of extra-framework aluminum oxide species is also seen in neutron powder diffraction data from proton- and deuterium-exchanged samples. The differences between results from the different analytical methods are discussed, and the novelty of direct proton counting by INS in this typical commercial catalyst is emphasized.

CeO2-doped WO3 composite catalyst based on acid site enhancement for diesel exhaust gas denitration

Based on the complicated preparation of current diesel vehicle exhaust gas denitration catalysts, an in-situ deposited composite oxide catalyst, CeO2-WO3 mixed oxide catalyst, was prepared by electrodeposition and hydrothermal methods, which was loaded on the titanium mesh and applied to the selective catalytic reduction denitration of diesel vehicle exhaust. Denitration performance of the catalysts was tested by a fixed bed reactor, and the influence of different electrodeposition time of CeO2 was investigated. The results demonstrate that 20 min is the best electrodeposition time of CeO2 (100% NOx conversion at 250–350 °C). The high dispersion of active CeO2 on WO3 promotes the synergistic effects among different components. The as-prepared catalysts were characterized by SEM, XRD, XPS, H2-TPR, NH3-TPD and in-situ DRIFTS. It is evident that Ce3+ is successfully introduced by loading CeO2, which enhances the chemisorption of oxygen. Meanwhile, the increased acidity including both weak acid and medium-strong acid sites of CeO2-WO3 composite catalyst is observed, which improves the co-adsorption of NH3 on Lewis acid and Brønsted acid simultaneously and facilitates the denitration process. Through the characterization by in-situ DRIFTS, it is elucidated that the NH3-SCR reactions are mainly carried out following the Eley-Rideal (E-R) pathway in a medium-temperature range (250–350 °C).

Reaction regeneration cycle of Mo/HZSM-5 catalyst in methane dehydroaromatization with the addition of oxygen-containing components

Reaction regeneration cycle of methane dehydroaromatization (MDA) with oxygen-containing gas components was studied. XRD, BET, Raman, NH3-TPD, O2-TG/DTG, TEM and 27Al-NMR were used to monitor textural structure, Mo species, and acid sites of catalyst before and after regeneration. Addition of oxygen components can extend reaction time per pass but cannot prevent the deactivation of regenerated catalyst. MoO3 species, acidity, and texture properties of Mo/HZSM-5 was identical after first regeneration, which may account for complete recovery of methane conversion and aromatic formation. During regeneration, the inevitable increase in Mo species size disrupts carbon deposition and significantly reduces methane dissociation. The crystallinity and number of strong acid sites of Mo/HZSM-5 catalyst decreased to a stable level before the collapse of zeolite framework without hindering aromatic formation. The recovered large-sized Mo species may accelerate the collapse of zeolite framework, irreversibly destroying Mo/HZSM-5 catalyst.

Enhanced catalytic ozonation of toluene using supported MnOx/USY via regulating the distribution of aluminum species in USY by dealumination

Recently, the problem of VOCs pollution has become serious in many regions, especially developing countries. Herein, the distribution of aluminum species in USY was controlled by dealumination of Y zeolite under different conditions, and then the dealuminated samples were used to prepare five different supported catalysts MnOx/USY to achieve high-efficiency catalytic ozonation of toluene at low temperature. It was found that aluminum species were successfully leached from the zeolite framework to the extra-framework, which changed the properties of the manganese oxide nanoparticles loaded on the zeolite. Moreover, the oxygen vacancies and the acid sites in different catalysts showed great differences. As the extra-framework aluminum species increased, the amount of oxygen vacancies in the catalysts decreased, while the content of acid sites exhibited a “volcano-type” trend similar to toluene conversion. The best catalysts (Mn-Y-3) maintain > 90% toluene conversion at 30 °C but the worst catalysts (Mn-Y-5) deactivate rapidly. With the help of in situ DRIFTS, it is found that the activation ability of toluene on the acidic sites of the catalyst is the key to the toluene conversion when the amount of oxygen vacancies is sufficient to decompose ozone into active oxygen species, and the contribution of Lewis acid sites is greater than Brønsted acid sites. It provides some theoretical guidance in designing effective catalysts for ozone catalytic oxidation of VOCs.

Sulfamic acid–modified zeolitic imidazolate framework (ZIF-90) with synergetic Lewis and Brønsted acid sites for microalgal biodiesel production

In order to enhance acidic sites in catalysts to improve conversion efficiency of microalgal lipids into biodiesel, an efficient bifunctional catalyst with synergetic Lewis and Brønsted acid sites was synthesized by modifying zeolitic imidazolate framework (ZIF-90) with sulfamic acid (SA). The sulfamic acid that combined with ZIF-90 through imine bond (CN) provided protons and destroyed coordinated Zn-N bonds in ZIF-90, thereby enhancing the number of Brønsted and Lewis acid sites. The total acidity of optimal catalyst increased from 0.478 to 0.848 mmol/g, while ratio of Brønsted acid to Lewis acid increased from 0.32 to 0.49. The Lewis acid sites in bifunctional catalysts exhibited higher activity towards transesterification reactions of triglycerides in microalgal lipids, while Brønsted acid sites exhibited higher activity towards esterification reactions of free fatty acids. Therefore, the optimal catalyst (weight ratio of SA to ZIF-90 was 0.05) promoted conversion efficiency of microalgal lipids into biodiesel from 80.6 % to 98.3 % at 200 °C, while conversion efficiency remained 91.7 % after 6 reusability cycles.

Co-pyrolysis of beech wood and polyamide-6: Effect of HZSM-5 catalyst on the properties of pyrolysis oils

Biomass residues and waste can be converted into bioliquids by pyrolysis, which can contribute to both the production of renewable fuels and the recycling of waste. In this paper, the pyrolysis of pure beech wood (BW) and of a mixture of BW + polyamide-6 (PA6), a nitrogen-containing plastic, was investigated to assess the effect of PA6 on the properties of bio-oils, obtained either by thermal pyrolysis or by pyrolysis with ex-situ catalytic treatment of the vapors. The presence of 20 wt% PA6 in the blend affected the pyrolysis products yields and distribution (gases, liquids, chars), but also the composition of the bioliquids. In absence of a catalyst, the production of phenolic compounds (guaïacol, syringol…), sugars, furans decreased significantly with the BW+PA6 blend compared to pure BW, and N-containing compounds derived from PA6 were found in the bioliquids. When HZSM-5 catalyst was applied for the treatment of vapors, a beneficial effect of the catalyst on the reduction of the sugars and furans content in the bioliquids and on the production of deoxygenated compounds was observed with pure BW. This effect was mitigated with BW+PA6 blends and the formation of fully deoxygenated compounds was almost totally suppressed, suggesting that the strong catalyst acid sites were poisoned. Caprolactam was by far the main product of PA6 degradation found in the bioliquids, but the N-containing by-products were different depending on the absence or presence of HZSM-5 catalyst. In particular, the formation of 5-cyano-1-pentene in a fairly large proportion was only observed in the presence of the catalyst.

Catalytic fast pyrolysis of cellulose over different metal-modified ZSM-5 zeolites for light olefins

Light olefins (C2H4, C3H6 and C4H8) are important chemical building blocks in modern energy and material system. In this study, the effects of different metal-modified ZSM-5 catalysts on the production of light olefins from cellulose fast pyrolysis were investigated in a fixed bed. Fe, La, Cu, Mg, Al and Ce modified ZSM-5 were prepared by the impregnation method, and then the derived modified ZSM-5 catalysts were characterized by different analytical instruments. The correlation between catalyst characteristics and the production of light olefins was explored. The results showed that the specific MFI-type structure of ZSM-5 remained intact after modification, and the surface area, pore volume and the amount of acid sites of catalysts varied. The highest light olefins yield was obtained over Cu-ZSM-5 (7.64 C-mol%), while the lowest was achieved over Mg-ZSM-5 (3.75 C-mol%). Moreover, the formation of light olefins can be promoted with the increasing of ZSM-5 other-pore volume and surface area, medium and strong acidity, and the decreasing of micro-pore volume and surface area, weak acidity. The results may share some light on the design of high efficiency ZSM-5 catalyst for high light olefins production.

Construction of framework confined ordered mesoporous Pt/TixAlOy catalysts and applied for the catalytic oxidation of propane

The framework confined Pt/TixAlOy catalysts were prepared by a one-step evaporation-induced self-assembly (EISA) technique, and their activities for the catalytic oxidation of propane were investigated. The Pt/TixAlOy catalysts exhibited high specific surface area due to the ordered mesoporous structure. With the increase of TiO2 contents, the specific surface area and acidic sites of Pt/TixAlOy catalysts increased. The specific surface area and acidic sites could improve the exposure of the active sites and electron transfer of Pt and TiO2, which was beneficial to catalytic oxidation of propane. However, too high acidic sites of catalysts could lead to coke deposition and clogging of the pores, and the addition of TiO2 had the optimal value. The Pt/Ti0.1AlOy catalyst exhibited superior catalytic activity, which could be attributed to the higher specific surface area, higher the percentage of Pt2+ and lattice oxygen, abundant acid sites, and higher redox properties. In addition, the Pt/Ti0.1AlOy catalyst also exhibited superior sulfur resistance due to the multiple acidic sites of catalysts.

Modulating the Acidic Properties of Mesoporous Mox–Ni0.8Cu0.2O Nanowires for Enhanced Catalytic Performance toward the Methanolysis of Ammonia Borane for Hydrogen Production

Rational construction of inexpensive, highly efficient, and stable catalysts for ammonia borane (AB) methanolysis is in high demand but still remains a great challenge. In this work, we have successfully fabricated uniform Mox-Ni0.8Cu0.2O nanowires using a simple hydrothermal method followed by a post-calcination treatment and flexibly modulated the acidity of their surface by changing the amount of Mo introduced into Ni0.8Cu0.2O. The Mo0.1-Ni0.8Cu0.2O catalyst displayed strong catalytic activity toward AB methanolysis with an ultrahigh turnover frequency of 46.9 molH2 molcat.-1 min-1, which is even higher than some noble metal catalysts. In this work, an equation regarding the relationship between the quantity of moderated acid sites of catalysts and its corresponding activity toward AB methanolysis was first determined. A plausible mechanism for AB methanolysis catalyzed by Mox-Ni0.8Cu0.2O was proposed, and the benefits of the introduction of MoO3 to Ni0.8Cu0.2O for enhancing the catalytic performance were also discussed. These findings can form a basis for the rational construction of inexpensive catalysts with robust performance toward AB methanolysis for hydrogen production.

Efficient nickel‐based catalysts for amine regeneration of CO2 capture: From experimental to calculations verifications

AbstractHigh heat duty is an urgent challenge for industrial applications of amine‐based CO2 capture. The temperature (>110°C) of carbamate breakdown in amine regeneration requires large energy consumption. In this work, we report a novel, stable, efficient, and inexpensive Ni‐HZSM‐5 catalyst to improve the CO2 desorption rate and reduce the heat duty. The impregnation method was applied for varying nickel content in the catalysts from 2.16 to 9.80 wt% in HZSM‐5. The catalysts were characterized by scanning electron microscope, X‐ray powder diffraction, N2 adsorption–desorption, inductively coupled plasma‐optical emission spectrometry, ultraviolet‐visible diffuse reflectance spectroscopy, X‐ray photoelectron spectroscopy, NH3‐temperature programmed desorption (TPD), Infrared spectroscopy of pyridine adsorption, and Fourier transform infrared spectroscopy. The catalytic performance was evaluated by CO2 desorption of rich amine solvent at 90°C. It was found that the introduction of nickel increased the acid sites of catalysts compared with parent HZSM‐5. This phenomenon plays a key role on improving the CO2 desorption rate. The density functional theory (DFT) calculations successfully explain the catalytic performance. The catalytic activity associates with the combined properties of MSA × B/L × Ni2+. The 7.85‐Ni‐HZ catalyst presents an excellent catalytic activity for the CO2 desorption: it increases the amount of desorbed CO2 up to 36%, reduces the relative heat duty by 27.07% with the same reaction time, and possesses high stability during five cyclic tests. A possible catalytic mechanism for the Ni‐HZSM‐5 catalysts through assisting carbamate breakdown and promoting CO2 desorption is proposed based on experimental results and theoretical calculations. Therefore, the results present that the 7.85‐Ni‐HZ catalyst significantly accelerates the protons transfer in CO2 desorption and can potentially apply in industrial CO2 capture.

Acidity and Stability of Brønsted Acid Sites in Green Clinoptilolite Catalysts and Catalytic Performance in the Etherification of Glycerol

Natural zeolite clinoptilolite CLIN with a framework ratio of Si/Al ≥ 4 containing mainly potassium and calcium ions in its internal channel system was used as a starting material. The acidic HCLIN catalysts were prepared under soft conditions avoiding the use of environmental less-benign mineral acids. The starting material was ion exchanged using a 0.2 M aqueous ammonium nitrate solution at a temperature 80 °C for 2 h. The obtained NH4CLIN was converted into the acid HCLIN catalyst by calcination at 300–600 °C. The obtained samples were characterized by XRD, FTIR, SEM/TEM, AAS, and EDX element mapping. The state of aluminium and silicon was studied by 27Al- and 29SiMAS NMR spectroscopy. The textural properties of the catalysts were investigated by nitrogen adsorption and desorption measurements. The Brønsted acidity of the HCLIN catalysts was studied by temperature-programmed decomposition of the exchanged ammonium ions releasing ammonia as well as 1H MAS NMR, {1H–27Al} Trapdor, and {1H–27Al} Redor experiments. The strongly agglomerated samples were crystalline and thermally stable up to >500 °C. Although a part of the clinoptilolite framework is maintained up to 600 °C, a loss of crystallinity is already observed starting from 450 °C. The specific surface areas of the starting CLIN and ammonium exchanged NH4CLIN are low with ca. 26 m2/g. The pores are nearly blocked by the exchangeable cations located in the zeolite pores. The thermal decomposition of the ammonium ions by calcination at 400 °C causes an opening of the pore entrances and a markable increase in the specific micropore area and micropore volume to ca. 163 m2/g and 0.07 cm3/g, respectively. It decreases with further rising calcination temperature indicating some structural loss. The catalysts show a broad distribution of Brønsted acid sites (BS) ranging from weak to strong sites as indicated the thermal decomposition of exchanged ammonium ions (TPDA). The ammonium ion decomposition leaving BS, i.e., H+ located at Al–O–Si framework bridges, starts at ≥250 °C. A part of the Brønsted sites is lost after calcination specifically at 500 °C. It is related to the formation of penta-coordinated aluminium at the expense of tetrahedral framework aluminium. The Brønsted sites are partially recreated after repeated ammonium ion exchange. The catalytic performance of the acidic HCLIN catalysts was tested in the etherification of glycerol as a green renewable resource with different C1-C4 alcohols. The catalysts are highly active in the etherification of glycerol, especially with alcohols containing the branched, tertiary alkyl groups. Highest activity is observed with the soft activated catalyst HCLIN300 (300 °C, temperature holding time: 1 min). A total of 78% conversion of glycerol to mono and di ether were achieved with tert-butanol at 140 °C after 4 h of reaction. The mono- and di-ether selectivity were 75% and 25%, respectively. The catalyst can be reused.

Selective production of lignin-derived monomers from corn stover by tuning the acid and hydrogenation sites of aluminum phosphate catalysts

This work is dedicated to the selective conversion of lignin. A nickel, tin, and sulfur-doped aluminum phosphate zeolite catalyst was developed for the selective production of lignin-derived monomers. The acidity and hydrogenation sites of this catalyst can be flexibly adjusted, and it exhibits a high yield (26.7%) for monomers with a nearly 68.8% conversion of lignin at 235 °C. The results show that Brønsted acid can increase the conversion of lignin and has a high selectivity for trans-ferulic acid, while Lewis acid and hydrogenation sites can promote the production of monomers with low oxygen content. The excellent stability and simple preparation method provide the possibility for the application of this depolymerization technology. This work could be a reference for the development of lignocellulosic biomass.

Hierarchical zeolites as efficient catalysts for dehydration of substituted indanols

Hierarchical zeolites of different topology and morphology (Al-, Ga- and B-silicate zeolites of MOR, BEA, MFI and MTW structural types with the morphology of aggregated nanosheets, nanorods, or close to spherical nanoparticles) were evaluated in the dehydration of a homologous series of substituted 4-bromo-2-alkyl-2,3-dihydro-1H-indan-1-ols. The optimal strength of the catalyst's acid sites providing both high indanols conversion and selectivity towards indenes (up to 99%) was found for each of the studied substrates. Stronger acid sites than optimal ones resulted in the formation of by-products of self-alkylation of the initial indanols by the formed indenes or alkylation of benzene used as a solvent. Weak acidity of the catalysts led to low substrate conversion and the presence of the corresponding ether. A correlation between the catalyst acidity and the yield of the desired product was found. Medium strength acid sites were discovered to be preferable for the selective dehydration of substituted 4-bromo-2,3-dihydro-1H-indan-1-ol.

Water-mediated hydrogen spillover accelerates hydrogenative ring-rearrangement of furfurals to cyclic compounds

Upgrading bioderived furfurals (furfural, 5-hydroxymethylfurfural) to cyclopentanones (cyclopentanone, 3-hydroxymethylcyclopentanone) and cyclopentanols (cyclopentanol, 3-hydroxymethylcyclopentanol) is a representative bifunctional catalytic process in biomass conversion. Here, a class of Pd/NiMoO4 catalysts (Pd/NiMoO4-Cl, Pd/NiMoO4-AC) with low Pd loading (1.0 wt%) and different Pd dispersion are synthesized. The hydrogenation active sites and acidic sites of catalysts were adjusted by a water-mediated hydrogen spillover process. 56.3–85.3% yields of cyclopentanones and 65.4–85.2% yields of cyclopentanols were obtained by hydrogenative ring-rearrangement route of furfurals over Pd/NiMoO4-Cl and Pd/NiMoO4-AC, respectively. Over-hydrogenated byproducts (tetrahydrofurfuryl alcohol, 2,5-bis(hydroxymethyl)tetrahydrofuran) with a yield above 54% were generated by a full hydrogenation route over Pd/C. The difference in catalytic performance is results from alteration of the adsorption configurations of reactants and the transformation of Lewis acid sites to Brønsted acid sites by hydrogen spillover. This work presents an effective strategy for governing reaction routes and enhancing bifunctional catalysis with a hydrogen spillover mechanism.

Effects of Mg, Ca and K addition on Pt-Sn/γ-Al2O3 for propane dehydrogenation

Abstract: In the present study, the applicability of a bimetallic Pt-Sn/Al2O3 in propane dehydrogenation with different promoters, namely, Ca, Mg, incorporation of Mg-K and Ca-K was studied. The catalysts were prepared by the sequential impregnation of γ-alumina support and characterized by TPD, SEM, XRD and UV analysis. The propane conversion and propylene selectivity were evaluated under the representative industrial conditions. The results showed that the Pt-Sn-Mg-K/γ-Al2O3 catalyst had a better performance in terms of propane conversion and propylene selectivity and yield, due to the partially neutralize and synergistic effect of Mg and K (probably by increasing the platinum dispersion and preventing side reaction and coke formation). TPD results also showed the effects of all these promoters (Ca, Mg , Ca-K and Mg-K) on reduction of acidic sites of catalyst, which are favorable sites for cracking reaction and coke formation. In the meantime, Ca is more effective on reducing strong acidic sites, but also Mg is more effective on reducing weak and medium strength acid sites. Therefore, alkaline-earth metals and also using them with potassium could reduce side reaction products and lead to more selective reaction to propylene, and improve catalyst performance compared to industrial catalyst.