Zr Catalysts Research Articles

Conversion of Unprotected Aldose Sugars to Polyhydroxyalkyl and C-Glycosyl Furans via Zirconium Catalysis.

An efficient, zirconium-catalyzed conversion of unprotected aldose sugars with acetylacetone to polyhydroxyalkyl furans or C-glycosylfurans is reported. The furan products are formed in up to 93% yield using 5-10 mol % ZrCl4. Pentoses are readily converted at room temperature, while hexoses and their oligosaccharides require mild heating (i.e., 50 °C). Efficient conversions of glycolaldehyde, glyceraldehyde, erythrose, a heptose, and glucosamine are also demonstrated. This approach outpaces each of the previous Lewis acid-catalyzed methods in at least one the following ways: (i) lower catalyst loadings; (ii) reduced reaction temperatures; (iii) shorter reaction times; (iv) equimolar substrate stoichiometry; (v) expanded sugar scope; (vi) higher selectivities; and (vii) the use of an Earth-abundant Zr catalyst.

Cooperative Acid‐Base Sites of Solid Ba‐Zr Mixed Oxide Catalyst for Efficient Isomerization of Glucose to Fructose in Aqueous Medium

AbstractEfficient and highly selective isomerization of glucose to fructose was achieved by using the inexpensive Ba−Zr mixed metal oxide catalyst. Catalyst was prepared by varying Ba−Zr ratios using co‐precipitation method. Various phases formed, planes exposed, morphology, elemental composition and particle size, basic site density and strength, oxidation state of elements were well studied by using various characterization techniques. The XRD analysis clearly indicates the presence of Ba+2 and Zr+4 in the form of BaO, ZrO2 and BaZrO3 phases. The SEM and HR‐TEM images indicate that, Ba−Zr (2 : 1) catalyst prepared showed uniform morphology with spherical and rod‐shaped particles ranging from 300 to 600 nm. Under the optimized reaction conditions Ba−Zr (2 : 1) catalyst exhibited excellent results in terms of 57 % of glucose conversion with 89 % selective formation of glucose. The presence of both acidic as well as basic sites play vital roles in activating the substrate molecules to selectively yield fructose. Ba−Zr (2 : 1) catalyst showed excellent recyclability performance up to four recycles.

Reaction Mechanism of H2-Assisted C3H6-SCR over Ag-CexZr Catalyst as Investigated by In situ FTIR

A series of silver-doped cerium zirconium oxide(Ag-CexZr) samples was synthesized successfully for selective catalytic reduction of nitric oxide(NO) with hydrogen and propene(H2/C3H6-SCR) under excess oxygen condition. The catalytic activity test proved that Ag-Ce0.4Zr exhibited the best C3H6-SCR activity. Hydrogen(H2) significantly enhanced NO conversion and widened the temperature window. Multi-technology characterizations were conducted to ascertain the properties of fabricated catalysts including X-ray diffraction(XRD), Fourier transform infrared spectrometry(FTIR), scanning electron microscopy(SEM) and H2 temperature programmed reduction (H2-TPR). In situ FTIR results demonstrated that various types of nitrates and chelating nitrite were generated on Ag-CexZr after introduction of NO. Besides, adding H2 could increase the concentration of bidentate nitrate and chelated bidentate nitrate dramatically, especially for Ag-Ce0.4Zr catalyst. Transient reaction between pre-adsorbing NO and C3H6/C3H6+H2 illuminated that the most active intermediate was chelating nitrite,which was promoted significantly by H2 participation. Furthermore, adding H2 improved the formation of organo-nitro(R-NO2), which was the key intermediate in C3H6-SCR. The reaction mechanism over Ag-CexZr catalysts was proposed at 200 °C as follows: nitric oxide(NO)+propene(C3H6)+hydrogen(H2)+oxygen(O2)→chelating nitrite(NO2−)+acrylate-type species(CxHyOz)→organo-nitro(R-NO2)→isocyanate(—NCO)+cyanide(—CN)→nitrogen(N2).

Bifunctional Silicotungstic Acid and Tungstophosphoric Acid Impregnated Cu–Zn–Al & Cu–Zn–Zr Catalysts for Dimethyl Ether Synthesis from Syngas

In the present study, a set of methanol synthesis catalysts with different Cu/Zn/Al or Cu/Zn/Zr molar ratios were synthesized by a co-precipitation method. Silicotungstic acid and tungstophosphoric acid were impregnated into these materials to synthesize new bifunctional catalytic materials to be used in direct synthesis of dimethyl ether (DME) from syngas. In the case of methanol production, synthesized Cu/Zn/Al catalysts exhibited quite high methanol selectivity, reaching to approximately 87%. These results indicated that the dispersion of copper particles profoundly affected the selectivity of methanol. Direct synthesis of DME was investigated in the presence of heteropoly acid impregnated copper-based novel hybrid type bifunctional catalysts. Results revealed that product distributions were strongly influenced by the reaction temperature, pressure, heteropoly acid content, and type. Results proved that silicotungstic acid (STA) impregnated bifunctional catalysts showed much better catalytic performance than the tungstophosphoric acid (TPA) impregnated ones in DME synthesis from syngas. Very high dimethyl ether selectivity values were achieved in direct synthesis of dimethyl ether over the 25%, and 30% STA impregnated methanol synthesis catalysts, at 275 °C and 50 bar. DME selectivity presented an increasing trend due to the increase in heteropoly acid content over methanol synthesis catalysts. The silicotungstic acid incorporated (30%) Cu/Zn/Al catalyst, having a composition of 6/3/1 (30STA@CZA:631), showed the highest CO conversion and DME selectivity. However, coke formation over this catalyst was much more than the catalyst containing 25% STA. This is mainly due to the higher Bronsted acidity of 30STA@CZA:631 than 25STA@CZA:631. Low coke formation, together with quite high DME selectivity values achieved with 25STA@CZA:631, is a worthy distinction of this catalyst for the direct synthesis of DME from synthesis gas. Novel hybrid type catalysts are successfully synthesized for direct synthesis of dimethyl ether process. Heteropoly acid incorporated methanol synthesis catalysts are very active and stable in the direct synthesis of dimethyl ether process. Silicotungstic acid (STA) impregnated copper-based catalyst exhibits a superior performance than the tungstophosphoric acid impregnated catalyst.

Utilization of waste crude glycerol for hydrogen production via steam reforming over Ni–La–Zr catalysts

The biodiesel industry generates crude glycerol (CG) at the rate of 10% of the amount of biodiesel produced. With the production of this biofuel increasing, a large amount of CG is produced each year. This results in low price for it and its final disposal becomes a significant problem. Herein, steam reforming represents a viable route to valorize this biodiesel by-product into hydrogen. The performance of Ni–La–Zr catalysts (15 wt%) for steam reforming of a CG without any purification treatment has been investigated at atmospheric pressure and at 500 °C and 650 °C. These materials were prepared using a coprecipitation method with oxalic acid. At 650 °C, the catalyst calcined at 850 °C presents higher catalytic activity and stability and displays better resistance to deactivation by carbon formation than the catalyst calcined at 700 °C. This behavior can be attributed to several causes: higher surface nickel content, higher catalyst reducibility and the presence of oxygen vacancies formed as a consequence of the partial substitution of nickel atoms into the pyrochlore structure during the formation of the biphasic system, which is related to mechanisms that act in the removal of carbon deposits on the catalyst.

MPV reduction of ethyl levulinate to γ-valerolactone by the biomass-derived chitosan-supported Zr catalyst

Biomass-derived chitosan-supported Zr catalyst with dual acid–base properties exhibits highly efficient performance towards MPV reduction of ethyl levulinate to γ-valerolactone.

Methane dehydroaromatization over Fe-M/ZSM-5 catalysts (M= Zr, Nb, Mo)

Abstract The effect of the co-impregnation of fifth period transition metals (Zr, Mo and Nb) with Fe on ZSM-5 for the methane dehydroaromatization at 750 °C was studied. Characterization tests of XRD, TPR-H2, surface area (BET), TPD-NH3, SEM/TEM, FTIR and TPO were used to enlighten the catalytic properties and the coke formation. The strength and type of acid sites look similar, however the TPR results show that the co-impregnated metals influenced significantly the reducibility of Fe. Samples with Mo and Nb interact more strongly with Fe, while Fe–Zr present a reduction profile similar to the pure Fe supported on ZSM-5. The Fe–Zr catalyst decreases the induction period and controlled the coke deposition showing the most promising results for long term reactions.

Preparing a novel gradient porous metal fiber sintered felt with better manufacturability for hydrogen production via methanol steam reforming

The porous copper fiber sintered felts with gradient porosity structure (gradient PCFSFs) as catalyst supports is beneficial for heat and mass transfer for methanol steam reforming (MSR). However, the previously developed gradient PCFSF based on the velocity distribution introduces curved interface between different porosity portions, making the mold pressing method for its preparation more sensitive to tiny process changes. To improve its manufacturability, a novel gradient PCFSF with planar interface (PCFSF-SLR) is proposed in this paper by fabrication with multi-step mold pressing and solid phase sintering method using cutting copper fibers. Furthermore, MSR experiments under different gas hourly space velocities and reaction temperatures are conducted to verify the characteristics of PCFSF-SLR loaded with Cu/Zn/Al/Zr catalyst. The results have shown that the reaction characteristics of the PCFSF-SLR were similar to those with curved interfaces, and PCFSF-SLRs with a middle portion porosity of 0.9 have better hydrogen production performance and lower carbon monoxide concentration. More importantly, the results indicated that the methanol conversion and hydrogen flow rate of the gradient PCFSF with planar interface and porosity of 0.7-0.9-0.8 were close or even almost the same with that of the best gradient PCFSFs with curved interface and porosities of 0.7-0.9-0.8 and 0.8-0.9-0.7. Therefore, the proposed PCFSF-SLR provides a superior alternative to gradient PCFSFs with better manufacturability.

A facilitated synthesis of hierarchically porous Cu–Ce–Zr catalyst using bacterial cellulose for VOCs oxidation

Highly active CuO–CeO2–ZrO2 catalysts were prepared by sol-gel method, using environmentally friendly bacterial cellulose (BC) as structure directing regent.The catalyst designed with commercial BC (Com-BC) exhibited catalytic performances in toluene (T100 = 220 °C) and ethyl acetate oxidation (T100 = 170 °C) superior to the catalysts prepared by traditional methods. Furthermore, excellent stability was obtained and no deactivation was observed during the 100 h on stream in toluene and ethyl acetate oxidation at T100. The excellent activity and stability of Com-BC can be explained by the hierarchically porous structure, abundant oxygen vacancies, and good reducibility.

Novel copper foam with ordered hole arrays as catalyst support for methanol steam reforming microreactor

Methanol steam reforming microreactor is regarded as one of the effective approaches for online hydrogen source for fuel cells and the catalyst support is one of the most important component of microreactors. However, there is great room to improve the performance of microreactor by optimizing the structure of catalyst support. In this study, copper foams with different types of hole arrays were used as catalyst supports for constructing a new type of cylindrical laminated methanol steam reforming microreactor for hydrogen production. A laser processing method was used to fabricate the copper foams with hole arrays and a two-layer impregnation method was used to load the Cu/Zn/Al/Zr catalysts. The sphere-cut tetrakaidecahedrons model of copper foam was established and macroscopic numerical analysis were used to analyze the reactants distribution in copper foams. The optimal distribution of hole arrays of the copper foam was obtained by investigating the reaction characteristics under different flow rates of the reactant, reaction temperatures, and loading amounts of catalyst. The experimental results show that the microreactor for hydrogen production using copper foam with ordered hole arrays shows the higher methanol conversion and hydrogen flow rate comparing the ones without hole array. Because of improvement of the radial distribution uniformity and increase of the axial flow rates of the reactants, the best reaction performance of microreactor for hydrogen production is obtained when the copper foam with the configuration in which the hole size decreases along the radial and axial direction.

Glycerol Esterification to Glyceryl Diacetate over SO42−/W‐Zr Complex Solid Super Acid Catalysts

AbstractA series of SO42−/W−Zr catalysts with different W/Zr mole ratios were synthesized by solvent evaporation self‐assembly followed by impregnation of sulfuric acid. The catalysts were examined in the glycerol esterification with acetic acid, and fully characterized by XRD, BET, TEM, XPS, NH3‐TPD, H2O‐TPD and pyridine adsorption infrared spectroscopy. The results revealed that W/Zr mole ratio and calcination temperature significantly affected the structure, acidity and catalytic performance of the catalysts. SO42−/W−Zr(1:1)‐500 (with a W/Zr mole ratio of 1:1, calcined at 500 °C) exhibited the highest catalytic activity, which is mainly due to the fact that the catalyst had more acidic sites and good water tolerance. In addition, the catalyst also showed excellent recyclability, in five repeated runs the conversion of glycerol and yields of products remained stable.

Biogas to methanol: A comparison of conversion processes involving direct carbon dioxide hydrogenation and via reverse water gas shift reaction

Methanol is a clean fuel and an important intermediate in chemical synthesis. In this work, the synthesis of methanol from a large-scale biogas plant utilizing biomass in the form of animal, food and dairy wastes and wastewater sludge is studied. It considers upgrading the biogas into biomethane through a separation step to remove CO2 prior to steam reforming and produces syngas for methanol synthesis. Instead of rejecting to the atmosphere, the separated CO2 is mixed with the syngas from the reformer and fed to the methanol reactor. Three process schemes are simulated (using two different catalysts) and compared on the basis of maximum CH4 conversion and methanol productivity. While one of the catalysts is a conventional catalyst preferred for a CO-rich syngas feed, the second catalyst is designed for direct hydrogenation of a CO2-rich syngas feed. The process alternatives use reverse water gas shift reaction, direct CO2 hydrogenation and intermediate water removal. From the different cases considered, the maximum possible methanol production is 2100 tons per day from a biogas feed of 1.8 × 106 Nm3/year – this corresponds to a process of steam methane reforming followed by direct CO2 hydrogenation using Cu/Zn/Al/Zr catalyst (two methanol reactors in series with intermediate water removal between them.) It was also shown that all the three processes can be designed to be self-sufficient in meeting their electricity requirements without the use of any external fuel like natural gas, etc. Since we are converting waste to energy utilizing biomass and don't require any additional fossil fuels, this can be referred to as a clean and green production process.

Comparative Study on Dry Reforming of Methane Over Co-M (M=Ce, Fe, Zr) Catalysts Supported on N-Doped Activated Carbon

Comparative Study on Dry Reforming of Methane Over Co-M (M=Ce, Fe, Zr) Catalysts Supported on N-Doped Activated Carbon

A New Lewis Acidic Zr Catalyst for the Synthesis of Furanic Diesel Precursor from Biomass Derived Furfural and 2-Methylfuran

Herein, we reported the first time to use Lewis type acidic Zr/SBA-15 catalyst for the hydroxyalkylation/alkylation (HAA) reaction of biomass derived furfural and 2-methylfuran (2-MF) to produce diesel precursors. Characterizations such as XRD, XPS, SEM and TEM, were used to provide detailed structure features of mesoporous catalysts of varied Si/Zr ratios. Among the catalysts, Zr/SBA-15(20) (Si/Zr ratio(mol:mol) = 20:1) possessed the highest catalytic activity in the HAA reaction, providing 93.9% yield of the target product at 140 °C under neat condition. Lewis acid was revealed as the dominant active sites for the HAA reaction. Reaction parameters including reaction temperature, catalyst loading and furfural/2-MF ratio were investigated and found to affect the reaction efficiency and product yields. Besides, the optimal Zr/SBA-15(20) catalyst maintained outstanding recyclability in the recycling test, offering almost comparable reaction yields as freshly prepared catalyst. This work not only opens up a new concept by using Lewis catalyst for HAA reaction to synthesize diesel precursors from biomass, but also enriches the catalyst inventory of HAA reaction by providing a pH-neutral, recyclable and stable catalyst.

Enhanced Transfer Hydrogenation Activity of Zr‐Doped Mesoporous Silica through Sol‐Gel Method for the Reduction of Biomass‐Derived Unsaturated Carbon‐Oxygen Bonds

AbstractEfficient reduction of unsaturated functionalities of biomass derived molecules enables the production of new value‐added chemical. Herein, we reported a highly efficient and robust mesoporous silica catalyst (SBA‐15) doped with Zr metal sites for the reduction of biomass derived unsaturated molecules through transfer hydrogenation reaction. Specifically, ethyl levulinate was selected as model compound to investigate the reduction activities of the as‐prepared catalysts. An almost quantitative γ‐valerolactone (GVL) yield of 99%, through the ketone reduction and intramolecular cyclisation, was obtained at 160 °C for 18 h in the presence of hydrogenation donor 2‐Butanol (2‐BuOH). Comparative experiments among different type of Zr catalysts showed that the mesoporous structure of SBA‐15 was beneficial for maximizing the activity and the stability of the Zr sites though highly metal dispersion and metal‐chelation effect, respectively. Detailed studies on the catalyst characterization and optimization revealed the ratio of Si/Zr also affected the above reactivity. Mechanistic studies revealed that the interaction between polar C=O group was key to the reaction efficiency and poisoning experiments confirmed the existence of acid‐base sites for transfer hydrogenation process. The catalyst was also successfully recycled without much loss in reactivity. Finally, the catalyst was also applied to the reduction of a variety of unsaturated molecules with high yields.

Mn-based mixed oxides for low temperature NOx adsorber applications

Pd-promoted ternary oxides of the type Mn-Ce-Zr and Mn-Pr-Zr were characterized and evaluated for low temperature NOx storage applications such as diesel vehicle cold starts. While X-ray diffraction data were in all cases consistent with the formation of solid solutions, Mn/Zr and Mn/Ce(Pr) ratios found by XPS were consistently higher than the bulk values, indicative of an enrichment of Mn at the surface of the solids. Both sets of Pd-promoted mixed oxides showed remarkably high NOx storage efficiency in the range 80–160 °C, while a 1.8% Pd/Mn(27)-Ce(7)-Zr catalyst showed excellent NOx storage in simulated cold start experiments. Moreover, ramping the temperature to 370 °C in these experiments, simulating higher speed operation, resulted in near complete purging of stored NOx from the catalyst. NOx storage efficiency in isothermal storage experiments was found to improve with increasing Mn content for the 1%Pd/Mn(x)-Ce(7)-Zr series (x = 9, 18, 27 wt.%), DRIFTS measurements showing that relative to Ce-Zr mixed oxides, Mn incorporation favored NOx storage as nitrate. During temperature programmed desorption (TPD) two main desorption events were observed, corresponding to decomposition of nitrites (up to 200 °C), followed by loss of nitrates (⁓200–400 °C). Nitrates stored on Pd/Mn-Ce(Pr)-Zr mixed oxides desorbed during TPD at lower temperatures than for CeO2-ZrO2 mixed oxides, a finding attributed to the lower basicity of Mn compared to Ce. Hydrothermal aging of 1.8%Pd/Mn(27)-Ce(7)-Zr at 700 °C reduced NOx storage efficiency, although the catalyst was still able to store significant amounts of NOx. However, catalyst sulfation led to a large decrease in NOx storage efficiency and the efficiency could not be completely recovered with lean or rich desulfations at high temperatures.

New insights on the basicity of ZnAl–Zr hydrotalcites activated at low temperature and their application in transesterification of soybean oil

Abstract

Effect of calcination temperature on low-temperature NH3-SCR activity and the resistance of SO2 with or without H2O over Fe–Mn–Zr catalyst

Abstract A novel Fe–Mn–Zr was prepared by co-precipitation method and calcined at different temperature. The NO removal capacity, N2 selectivity and SO2 resistance with or without H2O over Fe–Mn–Zr were investigated in a fixed-bed microreactor. The results showed that the catalysts calcined at 400–600 °C exhibit 100% NO removal efficiency in the range of 170–360 °C. FMZ-500 shows a better tolerance to both 100 and 200 ppm SO2 than other samples and excellent resistance to H2O and can achieve over 93% NO removal efficiency in the presence of SO2 and H2O. FMZ-500 catalyst can completely recover NO removal capacity when SO2 and H2O shut off. When Fe–Mn–Zr is calcined at 700 and 800 °C, NO removal efficiency at 170 °C are 90% for FMZ-700 and 35% for FMZ-800 and their resistances to SO2 are very poor. When Fe–Mn–Zr is calcined at 400, 500 and 600 °C, MnO2, Mn2O3 and Fe2O3 are homogeneously dispersed and exist mainly in an amorphous state as well as similar reduction properties. When the calcination temperature increases to 800 °C, the crystallinity of oxides significantly increases and reduction temperatures shift from 318 and 413 °C to 420 and 478 °C. High temperature calcination causes the decrease of surface area and Lewisacid sites, corresponding to low NH3 adsorption.

Ordered mesoporous Cu–Ca–Zr: A superior catalyst for direct synthesis of methyl formate from syngas

It is still a big challenge to obtain both highly active and stable Cu-based catalysts for direct synthesis of methyl formate (MF) from syngas. To address the issue, we have designed and synthesized a series of ternary Cu–Ca–Zr catalysts, namely, the ordered mesoporous Cu–Ca–Zr catalyst prepared by one-pot evaporation-induced self-assembly (EISA) method, and the supported CuO/CaO–ZrO2 catalysts by impregnating with copper precursor or by immobilizing copper nanoparticles. In the latter two catalysts, the ordered mesoporous CaO–ZrO2 support was also prepared by the EISA method. The catalysts were characterized by techniques such as ICP, XRD, TEM, N2 isotherm adsorption-desorption, XPS and H2-TPR, and used for direct synthesis of MF. The results indicated that the catalyst prepared by one-pot EISA method, in which the CuO species are highly dispersed in frame of CaO–ZrO2, exhibits much better activity and stability as compared with the other two catalysts with most of CuO located on the outer surface of the CaO–ZrO2 support, because the former has a higher specific surface area, enhanced synergistic effect and stronger interaction between the CaO–ZrO2 support and CuO active constituent.

Synthesis and characterization of Zr-promoted Ni-Co bimetallic catalyst supported OMC and investigation of its catalytic performance in steam reforming of ethanol

This article presents simple method for the OMC-6%Ni-6%Co (ordered mesoporous carbon containing Ni and Co metallic nanoparticles) catalyst synthesis with high surface area and more proper bimetallic nanoparticle dispersion; prepared successfully by soft template hydrothermal method and different zirconium loadings (0.5, 1, 2 wt %) accomplished by impregnation method, which was known as a desired method for the metal dispersion. The catalysts with/without promoter, were characterized by XRD, FTIR and N2 adsorption-desorption isotherms, FESEM, EDS, EDS mapping, HRTEM and TPR techniques and investigated in steam reforming of ethanol (SRE) at 250–400 °C. XRD and BET results indicated that zirconium addition more than 0.5% wt, decreased the average mesopore diameter of catalysts, total pore volume and particles size. Also, it was stated that Ni2+ and Co2+ were caught by the RF/F127 network and further reduced into metallic Ni and Co nanoparticles during the carbonization. The Ni and Co nanoparticles were well-dispersed in the OMC walls. FTIR spectroscopy revealed that F127 left the structure and formed the porous structure. TPR analysis of OMC-6%Ni-6%Co/2%Zr sample, indicated that the sample is reduced easily at low temperatures. FESEM and HRTEM images showed that carbon was precipitated in the CNT form on spent catalyst samples surfaces and confirmed the position of Ni and Co bimetallic nanoparticles on the CNTs tip in the OMC-6%Ni-6%Co/2%Zr sample. 2% Zr-promoted bimetallic catalyst revealed appropriate catalytic performance for SRE, such as high activity, hydrogen yield and proper stability due to the synergistic catalysis of cobalt and nickel. Also, effective factors, such as H2O/EtOH molar ratio and gas hourly space velocity (GHSV) were investigated on the OMC-6%Ni-6%Co/2%Zr catalyst sample.