K-doped Catalysts Research Articles

Potassium and cobalt double-doped ferrierites as a new class of soot oxidation catalysts

Research efforts to develop an effective soot oxidation catalyst have intensified in recent years due to the increased awareness of the highly harmful effect of soot particles on the human health and the environment. Large-scale application of a developed catalyst calls for a cheap support material allowing for an effective dispersion and thus a decrease in the active phase loading. Zeolites, widely used in catalysis as active phase carriers, possess advantageous characteristics such as a uniform porous structure and large surface area. Furthermore, they are characterized by high availability, good price, and are environmentally friendly. Cobalt-based materials provide promising soot oxidation catalyst phases, and alkali doping can further enhance their activity. This study focuses on the optimization of the potassium loading in the potassium and cobalt double-doped ferrierites towards a new class of cheap and environmentally friendly soot combustion catalysts. The potassium doping of the ferrierite-supported cobalt spienel was optimized in the range of 0–14 wt%. The obtained materials were characterized in terms of their composition (XRF, XPS, XRD, Raman spectroscopy), morphology (SEM, TEM/EDX/FFT), and reducibility (H2-TPR), and tested in the process of soot oxidation in tight and loose contact modes. The strong promotional effect of potassium was discussed in terms of a significant modification of the catalyst electronic properties (work function studies) and supported by the potassium surface state studies by the alkali thermal desorption method (SR-TAD). It was found that the optimal potassium promoter dispersion leads to the lowest catalyst work function and its highest activity in soot combustion. The effect of nitric oxide was also investigated for selected catalysts. The opposite effect of NO on the activity of undoped and K-doped catalysts was discussed on the basis of in-depth spectroscopic studies. An enhanced formation of nitrate species was found on the surface of the K-containing catalyst which led to the stronger inhibiting effect of NO.

Atomic-level mechanism and microkinetics of HCHO oxidation over K-doped MnO2 catalysts

K-doped MnO2 is regarded as an efficient catalyst for HCHO oxidation. A combined study of density functional theory (DFT) and microkinetic modeling was implemented to investigate the role of potassium doping in the catalytic reactivity of MnO2 towards HCHO oxidation. The DFT-derived thermodynamic stability analysis indicates that the K-doped MnO2 surface is more stable than the pristine MnO2 surface under the practical experimental conditions. The introduction of K ion is energetically beneficial to the adsorption of HCHO and O2 by charge transfer from potassium to the catalyst surface. The HCHO oxidation paths show that the rate-determining step is the second dehydrogenation reaction. The best catalytic activity of MnO2@K-1 is associated with the abundant Mn atom with a high chemical valence on the catalyst surface. Specially, K doping has little effect on the adsorption of water, but promotes the production of OH group by reducing the energy barrier of hydrolysis. The hydroxylated surface is favorable for the two-step cleavage of the C-H bond. The overall reaction rate of HCHO oxidation on the K-doped MnO2 catalyst is much higher than that on the pristine MnO2. At low temperatures, the reaction rate is relatively insensitive to the pressure change, while the oxidation rate gradually rises with the increasing of pressure at high temperatures. K doping is conducive to boosting the reaction rate of HCHO oxidation, which is associated with the stronger interaction of reactants with K-doped catalysts.

Effect of Alkaline Additives over V-Based Catalysts Supported on y- Al2O3 for Propane Oxidative Dehydrogenation

The olefins product are more reactive than the corresponding alkanes, and may easily be super-oxidised into CO and CO2 in selective oxidation of alkanes. The proper balance of acid and base sites on the V-based catalyst surface plays a decisive role in limiting the complete oxidation of alkanes. Therefore, our goal was to evaluate the promoting effect of alkali metals and the support effect using boehmite as precursor for the propane oxidative dehydrogenation (ODH) reaction. Catalysts were prepared via co-impregnation of V and Na or K on a synthesized alumina support. The following characterization techniques were used: N2 adsorption-desorption, X-ray diffraction (XRD), temperature programmed reduction (TPR) and isopropanol decomposition testes to evaluate the acid-base character. The catalyst performance in the propane ODH reaction was evaluated at the O2:C3H8:He molar ratios of 5:2:4, 6:1:4, and 4:3:4. The K-doped catalysts exhibited higher propene selectivity owing to the modification of acid-base character that rendered the weaker interaction between olefinic intermediate and more basic catalyst surface. A high molar fraction of O2 of the reaction mixture minimized coke formation and a high reoxidation rate possibly increased catalytic activity and propene selectivity.

Soot combustion over CeO2 catalyst: the influence of biodiesel impurities (Na, K, Ca, P) on surface chemical properties.

This work assessed the impact of biodiesel impurities on CeO2 catalyst for soot combustion via soot-TPO experiments. The results showed that Na- and K-doped catalysts were assisted for soot combustion, while Ca- and P-doped catalysts had a negative effect. N2 adsorption-desorption and XRD results indicated that doping biodiesel impurities led to smaller surface area by blocking small pores. Surface chemical properties are suggested as major reasons for promoting soot combustion by means of XPS, H2-TPR, and O2-TPD. Na- and K-doped catalysts showed stronger redox ability and surface lattice oxygen mobility, poorly for Ca- and P-doped catalysts. Interestingly, a large number of surface oxygen species were observed on P-doped catalyst and it enhanced the ignition of bio soot. In the presence of NO, surface chemical properties including NOx storage/release capacity and NO oxidation ability were characterized by NO-adsorption DRIFTS, NO-TPO and NOx-desorption DRIFTS, alkali-doped catalyst with excellent NOx storage capacity that can release active oxygen species and gaseous NO2 accelerate heterogeneous soot combustion, and the poor NO conversion ability to NO2 that weakens the promotion effect of soot combustion. Particularly in the existence of P, the promotion effect of soot elimination in NO + O2 was further weakened by the reason of poor NOx storage capacity and NO oxidation ability.

Understanding of K and Mg co-promoter effect in ethylene oxychlorination by operando UV–vis-NIR spectroscopy

The comprehensive kinetic study for CuCl2/γ-Al2O3-based catalysts was performed to elucidate the co-promoter effect in the ethylene oxychlorination, one of the most significant industrial processes to produce vinyl chloride monomer. Kinetic analysis was performed separately by transient kinetic studies, taking account of the reduction and oxidation steps in the catalytic cycle. The promoter effects on ethylene oxychlorination were ascribed to their influence on the Cu2+ reduction or Cu+ oxidation in the catalytic cycle. The reaction rate-diagram was gained and used to predict the steady-state reaction rate and Cu oxidation state by an operando setup combing MS and UV–vis-NIR spectroscopy. The results indicated that the K-doped catalyst could greatly increase the reaction rate of the oxidation step, which gave rise to higher Cu2+ concentration on the catalyst. Mg-doped catalyst had a great effect on enhancing the reaction rate for the reduction step. K and Mg co-doped catalyst had the dual effect, both the reaction rate and Cu oxidation state were located between K and Mg mono-doped catalyst. The results of steady-state reactions indicated that the reaction rates were quite close with that predicated by the rate-diagram. Byproduct analysis during the steady-state was also performed, the results demonstrated that the co-promoted catalysts can also reduce the byproduct formation. The current study is expected to provide one way for exploring the potential benefits of co-promotion on CuCl2/γ-Al2O3-based industrial oxychlorination catalysts to improve the catalytic performance and understand the reaction further.

Study on oxidation activity of Ce\u2013Mn\u2013K composite oxides on diesel soot

As an effective method, diesel particulate filter (DPF) technology has a great contribution in reducing soot emissions from diesel engines. To achieve passive regeneration of DPF at low temperatures, K-doped Ce0.5Mn0.5O2 catalysts were synthesized using sol–gel method. The effect of K-doped catalysts-Kz–Ce0.5Mn0.5O2-on the oxidation of soot had been studied by thermogravimetric analysis, and the corresponding catalytic properties were evaluated based on X-ray diffraction (XRD), hydrogen temperature programmed reduction (H2-TPR), O2 temperature programmed desorption (O2-TPD) Raman spectroscopy (Raman), Brunauer–Emmett–Teller (BET) and Fourier-Transform-Infrared (FTIR).The results showed that K doping facilitated the oxidation of diesel particulate matter, which was indicated by the entire mass loss curve shifting to lower temperatures. K0.2–Ce0.5Mn0.5O2 showed the best performance among the series of K-doped catalysts. Compared with the findings for Ce0.5Mn0.5O2, the ignition temperature of soot oxidation (Ti) had been lowered by 28 ℃, and the maximum peak combustion temperature (Tm) of the dry soot decreased by 61 °C. Furthermore, compared with the Ce0.5Mn0.5O2-catalyzed reaction, K doping led to a lower activation energy and significantly improved pre-exponential factor. The minimum reaction activation energy of 27.46 kJ/mol was exhibited by K0.2–Ce0.5Mn0.5O2.

Effects of low molar concentrations of low-valence dopants on samarium oxide xerogels in the oxidative coupling of methane

The effects of low-valence dopants on the catalytic properties of samarium oxide xerogel catalysts were investigated in the oxidative coupling of methane (OCM). More specifically, very low concentrations (0.1 and 1.0 % by mol) of transition metal (Ag, Ni, and Cu) and traditional alkali metal (Li and K) dopants were investigated. At these low loadings, it was shown that transition metal dopants have potential to improve the activity and selectivity over an undoped Sm2O3 xerogel, but these dopants can only outperform alkali metal dopants under certain conditions. Even at a concentration of 0.1 mol %, the dopants significantly increased the number of basic sites compared with the pure Sm2O3 xerogel. However, no trend is evident between the number or strength of the basic sites and the activity or selectivity in the methane coupling reaction. The XRD data reveal a lattice expansion upon addition of the low valence dopants, which is consistent with substitutional doping and the formation of oxygen vacancies due to charge compensation. In most cases the majority of the dopant stayed in the lattice during reaction. The dopants were also shown to influence the Sm2O3 structure, and the dopants that were more effective in suppressing the transformation from cubic to monoclinic Sm2O3 in general resulted in the more active and selective catalysts. While the Ag- and Ni-dopants could outperform the alkali metal doped catalysts in narrow temperature ranges, the best performing catalysts were still the K-doped Sm2O3 catalysts, as the 1.0 % K catalyst exhibited the highest activity at the lowest temperature (500 °C) and the 0.1 % K-doped catalyst was the most stable during extended operation. These results indicate that transition metal dopants, at low concentrations, can positively affect the activity and selectivity of a methane coupling catalyst, such as Sm2O3, and suggests that there may be benefits to other OCM catalyst systems from traditionally non-selective dopants, as long as the concentrations are kept very low and stability issues are addressed.

Effect of Biodiesel impurities (K, Na, P) on non-catalytic and catalytic activities of Diesel soot in model DPF regeneration conditions

The impact of Biodiesel impurities (Na, K and P) on the non-catalytic and catalytic reactivity of Diesel soot was evaluated under model DPF (Diesel Particulate Filter) regeneration conditions. Temperature-programmed oxidation (TPO) measurements confirmed that Na and K depositing into soot or on the surface of the catalyst enhanced the oxidative reactivity of soot under both O2 and NOx + O2 and Na-doped samples showed better results. However, the presence of P inhibited the non-catalytic and catalytic reactivity. These findings can be mainly attributed to the changes in nanostructure and surface chemical properties of the doped samples, characterized by Raman, high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), H2 temperature-programmed reduction (H2-TPR) and NO temperature-programmed oxidation (NO-TPO). The result of this characterization evidenced that the presence of Na and K increased structural defects of soot and reduction ability of the catalyst. Moreover, Na-/K-doped catalysts presented higher oxidizing ability of NO into NO2, whereas the opposite trend was observed for the P-containing catalysts. In addition, higher structural disorder of Na-doped soot and higher alkali metal content on the surface of Na-doped catalyst might lead to enhanced reactivity in comparison to K-doped soot and catalyst.

NH<sub>3</sub>-SCR Performance and Applicability of Mn-Based Spinels over TiO<sub>2</sub> Catalyst

A series of Mn-based spinels over TiO2 catalysts have been prepared with the impregnation method. Catalysts were comprehensively characterized using XRD, FESEM, H2-TPR, and the activity evaluation of NH3-SCR, while long-time stability tests and the effect of H2O on NH3-SCR were also investigated. Meanwhile, K poisoning effect was studied by preparing K-doped catalysts (K-Mn/TiO2, K-Cu-Mn/TiO2, K-Mg-Mn/TiO2 and K-Co-Mn/TiO2). According to the characterizations, Cu-Mn/TiO2, Mg-Mn/TiO2 and Co-Mn/TiO2 catalysts exhibited superior low-temperature SCR activity, stability, K resistance and H2O resistance due to the formation of spinels (MgMn2O4, CoMn2O4, CuMn2O4).

Fe-MOF-derived highly active catalysts for carbon dioxide hydrogenation to valuable hydrocarbons

Fe-based catalysts were acquired by one-step Fe-MIL-88B pyrolyzation and it showed high catalytic performance on hydrogenated conversion of carbon dioxide to valuable hydrocarbons. The iron compositions and catalytic performance of the catalysts were determined by pyrolysis temperatures according to XRD, SEM, TEM, N2-physisorption, Raman and evaluation results. Magnetite was obtained at 773K while metallic iron was the main phase when the pyrolysis temperature increased to 973K. Different catalytic performances over these catalysts were attributed to the transformation of iron species under the reaction conditions. Olefin-to-paraffin ratio (O/P) over pyrolyzed and K-doped catalysts was 1.3 and 5.5, respectively, and the two samples exhibited CO2 conversion with 46.0% and 43.1%, respectively. Higher catalytic performance was achieved when certain amount of Fe3O4 and χ-Fe5C2 existed in catalysts whereas metallic iron and/or θ-Fe3C had detrimental effects on lower conversion of CO2 and selectivity of valuable hydrocarbons.

Promoter effect of alkalis on CuO/CeO2/carbon nanotubes systems for the PROx reaction

The effect of alkali promotion (Li, Na, K and Cs) on the CO preferential oxidation (CO PROX) reaction has been studied over Cu-CeO2 catalyst supported on carbon nanotubes (CNT). The catalysts were prepared with 2.5wt.% Cu and 20wt.% CeO2 loadings, and alkali/Cu atomic ratios of 0.68. The catalytic performance and the characterization by powder X-ray diffraction (XRD), TEM-STEM, H2-temperature-programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS) has been presented. TEM and XRD analyses showed that the addition of alkali reduces the size of ceria crystallites. It was found that in general the incorporation of alkali favored the conversion of CO at low temperatures, being more pronounced for the K-doped catalyst. The characterization showed that the addition of K favored the Cu-CeO2 interaction, the activity of the catalyst was enhanced and the opposite was observed for Cs-doped sample. The characterization results reveal that the observed increase in the Cu+ species proportion and in lattice oxygen are related to the better catalytic performance.

Formic acid decomposition over palladium based catalysts doped by potassium carbonate

The introduction of potassium carbonate into Pd/Al2O3, Pd/SiO2 and Pd/C catalysts promoted both the catalytic activities and the hydrogen selectivities for the vapor-phase formic acid decomposition, giving values of the turnover frequency (TOF) at 343K that were 8–33 times higher than those for the undoped samples. The apparent activation energies over all the K-doped samples increased considerably, this showing that there is a difference in the reaction path between the doped and the undoped catalysts. Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) has been used to gain an understanding of the nature of the species formed in the Pd/SiO2 catalysts during the reaction. This study showed that a considerable fraction of the HCOOH was condensed in the pores of the catalysts and that the introduction of potassium contributed to the formation of buffer-like solution. The existence of mobile formate ions present in the buffer solution and stabilized by K ions in a K-doped catalyst is an essential factor in the promotion of its activity.

La1−xKxFe0.7Ni0.3O3 catalyst for ethanol steam reforming—The effect of K-doping

Coking is the critical problem for catalysts for steam reforming of ethanol (SRE). Several techniques have been reported for improving the ability to prevent coking of catalysts, such as adding alkaline to balance the acidic sites on the support, using support which can generate oxygen vacancies and using bimetallic catalysts. In this work, we try to improve the ability to prevent coking of this kind of catalyst by doping additives to modify the active component, which has not been attracted attention for SRE catalysts yet. La1−xKxFe0.7Ni0.3O3 (x=0, 0.05, 0.1) with perovskite structure was prepared by citric acid complexation method, and after reduction K-doped Ni/LaFeO3 catalysts were obtained. The catalytic performance including the ability to prevent coking and sintering over the catalysts were investigated. The catalysts were characterized by using X-ray diffraction, transmission electron microscopy, thermal analysis techniques and X-ray photoelectron spectroscopy analysis. The results indicate that the K-doped catalysts are very active, highly selective to hydrogen, as well very stable for SRE reaction. The doping of potassium can also restrain the sintering of nickel. The doping of K improved the ability to prevent coking of the catalyst markedly, which is attributed to the electron donation effect of potassium to nickel and this donation effect can promote the ability for breaking CC bond on the metal nickel sites.

Adsorption microcalorimetry characterization of K-doped MgAl mixed oxide catalysts for soybean oil transesterification synthesized by impregnation and ball milling techniques

Layered double hydroxides were prepared by pH-controlled co-precipitation method with a Mg/Al molar ratio between 1.5 and 4.0 and used as precursors for obtaining, through calcination, a series of MgAl mixed oxides, which were used as catalysts for soybean oil transesterification with methanol. The mixed oxide with the highest Mg/Al ratio was doped with potassium for obtaining highly basic catalysts. Three different potassium salts (K2CO3, KNO3, CH3COOK) were used for loading potassium on the support (K loading ca. 3 mass%) by two different techniques, namely conventional incipient wetness impregnation and innovative mechanical milling. All the catalysts were characterized as to their chemical composition, structure and texture by inductively coupled plasma atomic emission spectroscopy, X-ray diffraction and N2 physisorption, respectively. Their basic and acid features were assessed by adsorption microcalorimetry, using CO2 and NH3 as probe molecules, respectively. Catalytic testing was carried out in a slurry batch reactor operated at 343 K and atmospheric pressure. The occurrence of potassium leaching into the liquid phase was checked for the K-doped catalysts. The initial activity of the heterogeneous catalysts was interpreted in terms of surface basicity, by taking into account a possible role of acidity in determining the mechanism.

K-doping of Co/Al2O3 low temperature Fischer–Tropsch catalysts

The effect of potassium doping on Co/Al2O3 Fischer–Tropsch catalyst has been investigated using in situ IR spectroscopic measurements and catalytic activity tests in flow reactor. The data confirm the inhibiting effect of K doping on reducibility and catalytic activity, together with a stabilization of the catalytic activity, a reduction of methane selectivity and a slight increase of CO2 selectivity.CO adsorbs over the Co/Al2O3 catalyst forming on-top surface carbonyls, responsible for a Infrared CO stretching band at a position more typical of fcc 100 face than of hcp 0001 face. In the presence of hydrogen CO adsorption shifts in part from terminal to bridging sites. Potassium doping significantly increases the electron donating ability of cobalt metal particles, as evidenced by the shift down of 15cm−1 of the CO stretching frequency of adsorbed carbon monoxide. CO adsorbed on surface defects is also evident. After CO adsorption at 250°C even lower frequency carbonyls are observed only on the K-doped catalyst (2000 and 1825cm−1) providing evidence of a stronger interaction of CO with the surface. At 250°C in the presence low pressure of CO+H2, methane, ethylene and other lower olefins form in the IR cell. The ethylene/methane molar ratio produced over the K-doped catalyst is definitely higher than over the K-free sample, suggesting that potassium favours the first chain growth step in the Fischer–Tropsch process thus allowing decreased selectivity to methane. Reasons for the increased catalyst stability are briefly discussed.

Stainless steel wire mesh-supported potassium-doped cobalt oxide catalysts for the catalytic decomposition of nitrous oxide

Structured catalysts consisting of potassium-doped cobalt oxide supported on stainless steel wire mesh were tested for the decomposition of N2O under dry and wet conditions. The cobalt oxide catalysts were prepared by the ammonia-evaporation-induced method. Of the several doping procedures tested, dropwise impregnation with potassium carbonate solutions provided the best catalytic results at lower K/Co molar ratios. Kinetic analysis of a potassium-doped catalyst yielded a reaction order on the N2O partial pressure slightly below unity (0.87). The activation energy values and the natural logarithms of the pre-exponentials factors for the different catalysts followed the classical compensation effect. This effect may be the result of a combination of competing reactions on different groups of active centers. Thus, cobalt ions affected by potassium display a low activation energy (∼40kJ/mol), whereas cobalt atoms unaffected by potassium display a higher activation energy equal to that of the undoped catalysts (∼106kJ/mol). The catalytic activity of the catalysts in N2O decomposition increases with the amount of reducible Co3+ ions, although there does not appear to be a direct relation between the amount of Co3+ ions and the textural and crystal properties of the catalysts. The addition of water produces some inhibition of the N2O decomposition reaction on K-doped catalysts, although catalytic activity is completely restored when the water is removed from the reaction stream. The catalysts prepared in this work were found to be among the most active, selective and stable catalysts reported in the literature.

Platinum supported on alkaline and alkaline earth metal-doped alumina as catalysts for dry reforming and partial oxidation of methane

Pt catalysts with low metal loadings (0.02, 0.1 and 0.5wt%) supported on alkaline (Na and K) or alkaline earth (Mg) metals-doped alumina were tested in the catalytic partial oxidation and dry reforming of methane. Supports were characterized by X-ray diffraction and also by determining their BET surface area, temperature-programmed desorption of CO2, and isopropanol dehydration; while catalysts were characterized by X-ray diffraction, temperature programmed reduction, tests of cyclohexane dehydrogenation, temperature-programmed oxidation, and transmission electronic microscopy. The presence of the dopants modified the thermal stability of the γ-Al2O3 phase by calcination at 1000°C and the acidity of the support. The γ→θ transition took place for K- and Na-doped catalysts, the acidity being almost suppressed. Conversely, the Mg-doped γ-Al2O3 was thermally stable, and the catalysts still showed some acidic sites. The catalytic performances in both partial oxidation and dry reforming processes were dependent on the support dopants, with a more notable effect observed at low-noble-metal loadings. K- and Na-doped catalysts showed poor activities in the catalytic partial oxidation reaction, whereas the presence of Mg in the alumina promoted the catalytic activity. In the dry reforming reaction an improvement was found in the catalytic activity for the sample with the highest Pt content; moreover, the K-doped catalysts were slightly more efficient.

Catalytic activity of alkali metal doped Cu-Al mixed oxides for N2O decomposition in the presence of oxygen

Three CuAl hydrotalcite-like compounds (CuAl-HLc) with Cu/Al atomic ratio of 2.0, 3.1 and 4.1 were prepared by a co-precipitation method and calcined to convert into CuAl mixed oxides. The CuAl mixed oxide with Cu/Al atomic ratio of 3.1 was incipiently impregnated by alkali metal (Na, K, Cs) salt solution to prepare the modified CuAl mixed oxide catalysts. The properties of the catalysts were characterized by AES, XRD, FT-IR, BET, H2-TPR and XPS techniques. The effect of CuAl mixed oxide compositions, alkali metal types and potassium precursors on catalytic activity for N2O decomposition in the presence of oxygen were investigated. It is revealed that the catalytic activity of CuAl mixed oxides impregnated by K2CO3 solution is higher than that of Na2CO3 and Cs2CO3 doped catalysts. In addition, the catalytic activity of CuAl mixed oxides can be largely enhanced by the addition of K species from the precursors of K2CO3 and K2C2O4, whereas KNO3- and CH3COOK-doped catalysts show a lower activity than sole CuAl oxide. The optimal K-doped catalyst exhibits a good activity for N2O decomposition in the presence of oxygen and steam.

Effect of potassium on physicochemical properties of CrO x/Al 2O 3 and CrO x/TiO 2 catalysts for oxidative dehydrogenation of isobutane: The role of oxygen chemisorption

Potassium addition has different influence on the selectivity to isobutene in oxidative dehydrogenation of isobutane for the two chromium based catalysts: the decrease for CrO x /Al 2O 3(CrAl) and the increase for CrO x /TiO 2(CrTi). This contrary effect of potassium was found to be associated with the increase in the rate of oxygen chemisorption (equivalent to the rate of reoxidation) and the increase in coverage with oxygen for CrAl, and with the decrease of these parameters for CrTi catalyst. Acid–base properties, determined by isopronanol decomposition and reducibility, estimated from TPR data, seem to affect less the catalytic properties, since they change on the potassium addition in the same way: acidity and reducibility decrease and basicity increases in the K-doped catalysts. Electron work function was found to decrease for potassium doped CrAl and did not change for CrTi catalyst.

A study of furfural decarbonylation on K-doped Pd/Al 2O 3 catalysts

Vapor-phase decarbonylation of furfural to furan was performed on K-doped Pd/Al 2O 3 catalysts in a fixed-bed reactor. A series of K-doped catalysts were prepared by impregnation method with various potassium salt precursors and different potassium content. The catalyst evaluation results revealed that the doping of K not only promoted the furfural decarbonylation, but also suppressed the hydrogenation side reaction. Among the investigated catalysts, Pd–K 2CO 3/Al 2O 3 (K% = 8 wt.%) presented the best performance and achieved the furan yields up to 99.5% at 260 °C. The selectivity of 2-methylfuran would approach zero at high K content (K% > 4 wt.%). Furthermore, the catalysts were characterized by BET, SEM, ICP, H 2-TPR, H 2-TPD, H 2-chemisorption, CO-FTIR, furfural-TPSR, and furfural-FTIR experiments. It was shown that the dopant phase had a remarkable effect on the precursor Pd 2+ and the reduced Pd metal particles. Furfural-TPSR and furfural-FTIR exhibited that K-doped catalysts enhanced the furfural adsorption and promoted the decarbonylation reaction, which was due to the different adsorption mode and intensity of furfural on K-doped and undoped samples. Besides, the decrease of C–O adsorption of furfural ( η 2(C,O)-furfural) by K doping is the main reason for suppressing the furfural hydrogenation.