Boosting the Ni-Catalyzed Hydrodeoxygenation (HDO) of Anisole Using Scrap Catalytic Converters

The large availability and renewable nature of lignin makes its upgrading to bioproducts of particular interest for sustainable development. The hydrodeoxygenation (HDO) of anisole specifically represents a model reaction for the conversion of lignin to biofuels through the removal of the aromatic carbon-oxygen bonds. To date, a range of Ni-based catalysts have been reported as highly active systems for the HDO of anisole. However, there has been a substantial lack of consideration given to the environmental characteristics of these catalytic systems, in contrast with the scope of the sustainable production of biofuels. Herein, Ni-based SiO2 catalysts are prepared by a solventless and highly efficient mechanochemistry approach, having a considerably lower environmental impact as compared to standard impregnation methods. Importantly, scrap catalytic converters (SCATs) are employed as co-catalysts, proving the possibility of enhancing the catalytic HDO of anisole, with a scarcely exploited waste material. The results demonstrate that the combined use of Ni/SiO2 as catalysts and Ni/SCATs as co-catalysts remarkably boosts the rate of the conversion of anisole up to more than 50% by achieving an almost complete conversion of anisole in only 40 min instead of at 200 °C and 4 MPa H2

Potassium-modified bifunctional MgAl-SBA-15 for aldol condensation of furfural and acetone

The aldol condensation of furfural and acetone followed by hydrodeoxygenation into bio-jet fuel range alkanes and bio-polyester diols has attracted intensive interest in recent years. Such sequential reactions require a careful tailoring of one or more catalysts consisting of metal and acid–base active sites that can efficiently promote the two step cascade aldol condensation and hydrodeoxygenation. Here, we have begun developing a prominent base catalyst for mild aldol condensation of furfural and acetone by synthesizing acid–base bifunctional MgAl-SBA-15 and further modifying it with potassium. The catalyst with the highest basic site loading of 0.27 mmol g−1 showed a furfural conversion of 83% and 99% total selectivity to products comprising 54% 4-(2-furyl)-4-hydroxy-butan-2-one (FAc-OH, a C8 alcohol intermediate) and 23% of each 4-(2-furyl)-3-buten-2-one (FAc) and 1,4-pentadiene-3-one,1,5-di-2-furanyl (F2Ac) (C8 and C13 aldol condensation products, respectively) after 3 hours of reaction, at 50 °C. Though a higher loading of potassium causes severe blockages of mesopores and inaccessible acid sites, the catalyst could still be regenerated by open-air calcination and be re-used for considerable cycles with fair catalytic performances. Overall, the present study can be the stepping stone for future investigations on further tuning of non-interfering active sites in SBA-15 to promote an efficient one-pot transformation of furfural and acetone via the two-step cascade aldol condensation and hydrodeoxygenation

Nanosized TiO2: a promising catalyst for the aldol condensation of furfural with acetone in biomass upgrading

Nanosized TiO2catalyst was successfully prepared by a simple green procedure and used in liquid phasealdol condensation of furfural with acetone, a key step in bio-fuel processing. In order to determinethe effect of calcination temperature on catalytic properties of TiO2, the as-prepared TiO2and calcinedTiO2(150–900◦C) were studied by XRD, BET, TPD-CO2/NH3, TGA/DTG and FTIR evaluation. The catalyticperformance of TiO2samples in aldol condensation of furfural with acetone was evaluated and comparedwith that of Mg–Al hydrotalcites and a BEA zeolite. These experiments showed that uncalcined TiO2possessed reasonable activity in aldol condensation of furfural to acetone and resulted in commonlyproduced condensation products. The observed catalytic behavior of TiO2could be competitive withthat reported for other inorganic solids. The calcination of TiO2resulted, however, in a decrease in itscatalytic activity due to extensive dehydration and surface dehydroxylation as well as due to changes oftextural properties resulting in a decrease in the amount of accessible active sites. Thanks to its advancedproperties, nanosized TiO2is a promising catalyst for aldol condensation of furfural with acetone andcould broaden possibilities for optimizing conditions for bio-fuel production

Effect of Calcination Atmosphere and Temperature on the Hydrogenolysis Activity and Selectivity of Copper-Zinc Catalysts

A series of CuZn catalysts with a Cu/Zn ratio of 1.6 was prepared by the calcination of a single precursor, CuZn-P consisting of an equimolar mixture of aurichalcite and zincian malachite, in three different calcination atmospheres (air, nitrogen, and hydrogen) at three temperatures (220, 350, and 500 °C). All catalysts were characterized by XRD and N2-physisorption to assess their phase composition, crystallite sizes and textural properties and tested in dimethyl adipate (DMA) hydrogenolysis in a batch reactor at 220 °C and 10 MPa H2. The XRD examination of these catalysts proved that both parameters, calcination temperature and atmosphere, affected the resulting phase composition of the catalysts as well as their crystallite sizes. In an oxidizing atmosphere, CuO and ZnO in intimate contact prevailed whereas in inert or reducing atmosphere both oxides were accompanied by Cu2O and Cu. The crystallite size of Cu2O and Cu was larger than the size of CuO and ZnO thus indicating a less intimate contact between the Cu-phases and ZnO in catalysts calcined in nitrogen and hydrogen. Catalysts prepared by calcination at 220 °C and CuZn catalyst calcined in the air at 350 °C significantly outperformed the other catalysts in DMA hydrogenolysis with a 59–78% conversion due to the small crystallite size and intimate contact between the CuO and ZnO phases prior to catalyst reduction. Despite the low DMA conversion (<30%), transesterification products were the main reaction products with overall selectivities of >80% over the catalysts calcined in nitrogen or hydrogen at least at 350 °C. The obvious change in the preferred reaction pathway because of the atmosphere calcination and temperature shows that there are different active sites responsible for hydrogenolysis and transesterification and that their relative distribution has changed

Physico-Chemical Properties of MgGa Mixed Oxides and Reconstructed Layered Double Hydroxides and Their Performance in Aldol Condensation of Furfural and Acetone

MgGa layered double hydroxides (Mg/Ga = 2–4) were synthesized and used for the preparation of MgGa mixed oxides and reconstructed hydrotalcites. The properties of the prepared materials were examined by physico-chemical methods (XRD, TGA, NH3-TPD, CO2-TPD, SEM, and DRIFT) and tested in aldol condensation of furfural and acetone. The as-prepared phase-pure MgGa samples possessed hydrotalcite structure, and their calcination resulted in mixed oxides with MgO structure with a small admixture phase characterized by a reflection at 2θ ≈ 36.0°. The interaction of MgGa mixed oxides with pure water resulted in reconstruction of the HTC structure already after 15 s of the rehydration with maximum crystallinity achieved after 60 s. TGA-MS experiments proved a substantial decrease in carbonates in all rehydrated samples compared with their as-prepared counterparts. This allowed suggesting presence of interlayer hydroxyls in the samples. Acido-basic properties of MgGa mixed oxides determined by TPD technique did not correlate with Mg/Ga ratio which was explained by the specific distribution of Ga atoms on the external surface of the samples. CO2-TPD method was also used to evaluate the basic properties of the reconstructed MgGa samples. In these experiments, an intensive peak at T = 450°C on CO2-TPD curve was attributed to the decomposition of carbonates newly formed by CO2 interaction with interlayer carbonates rather than to CO2 desorption from basic sites. Accordingly, CO2-TPD method quantitatively characterized the interlayer hydroxyls only indirectly. Furfural conversion on reconstructed MgGa materials was much larger compared with MgGa mixed oxides confirming that Brønsted basic sites in MgGa catalysts, like MgAl catalysts, were active in the reaction. Mg/Ga ratio in mixed oxides influenced product selectivity which was explained by the difference in textural properties of the samples. In contrast, Mg/Ga ratio in reconstructed catalysts had practically no effect on the composition of reaction products suggesting that the basic sites in these catalysts acted similarly in aldol condensation of acetone with furfural. It was concluded that the properties of MgGa samples resembled in a great extent those of MgAl hydrotalcite-based materials and demonstrated their potential as catalysts for base-catalyzed reactions

Understanding of the Key Factors Determining the Activity and Selectivity of CuZn Catalysts in Hydrogenolysis of Alkyl Esters to Alcohols

CuZn catalysts are perspective catalysts for esters hydrogenolysis, but more knowledge is needed to optimize their catalytic performance. In this work, we consider the impact of CuZn catalysts composition on their structure, activity, selectivity, and stability in esters hydrogenolysis. Four catalysts with various Cu/Zn ratio were synthesized by a co-precipitation and characterized in as-prepared, calcined, reduced, and spent state by XRF, XRD, N2 physisorption, CO2-TPD, NH3-TPD, and N2O chemisorption. XRD data revealed the effect of the composition on the size of Cu and ZnO particles. The catalytic performance was investigated using an autoclave. All catalysts exhibited high methyl hexanoate conversion about 48–60% after 3 h but their activity and selectivity were found to be dependent on Cu/Zn ratio. The conversion of methyl hexanoate and hexyl hexanoate was compared to explain the observed product selectivity. Moreover, the catalysts stability was investigated in three consecutive reaction cycles and correlated with changes in the size of constituent particles. Moreover, when different esters were tested, a slight decrease in conversion and increase in alcohol selectivity with a growth in molecule size was observed. Obtained results allow making a conclusion about the optimal composition that provides the good performance of CuZn catalysts in ester hydrogenolysis

CuZn catalysts superior to Adkins catalysts for dimethyl adipate hydrogenolysis

Industrial hydrogenolysis of esters to alcohols relies on the use of Adkins catalysts whose production and disposal is an environmental burden. This work is focused on CuZn catalysts that represent an ecological alternative to Adkins catalysts. Four CuZn catalysts with Cu/Zn atomic ratio ranging from 0.5 to 2.0 and single phase CuO and ZnO catalysts were prepared by co-precipitation and their hydrogenolysis activity was compared with a commercial Adkins catalyst. Dimethyl adipate was used to test the catalyst performance in a flow reactor at temperatures ranging from 175 to 205 degrees C and hydrogen pressure of 16 MPa. The increase in ZnO content was directly responsible for the reduction in copper crystallite size and increase in the catalyst specific surface area. The CuZn catalysts exhibited higher conversion than the Adkins catalyst despite their specific surface area declined during the experiments more significantly than that of the Adkins catalyst. Nonetheless, the TOF of CuZn catalysts exceeded that of the commercial Adkins catalyst.Web of Science1182178216

Effect of Calcination Atmosphere and Temperature on the Hydrogenolysis Activity and Selectivity of Copper-Zinc Catalysts

A series of CuZn catalysts with a Cu/Zn ratio of 1.6 was prepared by the calcination of a single precursor, CuZn-P consisting of an equimolar mixture of aurichalcite and zincian malachite, in three different calcination atmospheres (air, nitrogen, and hydrogen) at three temperatures (220, 350, and 500 °C). All catalysts were characterized by XRD and N2-physisorption to assess their phase composition, crystallite sizes and textural properties and tested in dimethyl adipate (DMA) hydrogenolysis in a batch reactor at 220 °C and 10 MPa H2. The XRD examination of these catalysts proved that both parameters, calcination temperature and atmosphere, affected the resulting phase composition of the catalysts as well as their crystallite sizes. In an oxidizing atmosphere, CuO and ZnO in intimate contact prevailed whereas in inert or reducing atmosphere both oxides were accompanied by Cu2O and Cu. The crystallite size of Cu2O and Cu was larger than the size of CuO and ZnO thus indicating a less intimate contact between the Cu-phases and ZnO in catalysts calcined in nitrogen and hydrogen. Catalysts prepared by calcination at 220 °C and CuZn catalyst calcined in the air at 350 °C significantly outperformed the other catalysts in DMA hydrogenolysis with a 59–78% conversion due to the small crystallite size and intimate contact between the CuO and ZnO phases prior to catalyst reduction. Despite the low DMA conversion (<30%), transesterification products were the main reaction products with overall selectivities of >80% over the catalysts calcined in nitrogen or hydrogen at least at 350 °C. The obvious change in the preferred reaction pathway because of the atmosphere calcination and temperature shows that there are different active sites responsible for hydrogenolysis and transesterification and that their relative distribution has changed

Podporují kovové oxidy Cu aktivitu jako katalyzátoru pro hydrogenolýzu?

The well-established ester hydrogenolysis process has to be further improved to reduce its high energy demand and to replace used Adkins CuCr catalysts by chromium-free alternatives. In this study, the copper-based catalyst was modified by ZnO, ZnO with Al2O3 or MgO to elucidate the metal-oxide influence on catalyst structure, activity, performance and stability in ester hydrogenolysis. The catalysts composition, structure and physico-chemical properties were examined by AAS, XRD, TPR, BET, N2O-RFC, TGA-MS, NH3-TPD and CO2-TPD. It was confirmed that copper itself possesses high intrinsic activity for ester hydrogenolysis but the unpromoted copper species were very unstable. All used metal oxides were proven to be structural promoters stabilizing copper species and increasing the number of active sites. Consequently, they enhanced remarkably catalyst performance in dimethyl adipate conversion despite the decreased intrinsic activity of Cu active sites. All prepared catalysts outperformed a commercial CuCr catalyst in dimethyl adipate hydrogenolysis.Byla studována účinnost modifikovaných Cu katalyzátorů v hydrogenolýze esteru. Modifikace byla provedena pomocí ZnO, ZnO s Al2O3 a MgO. Vliv modifikace na účinnost katalyzátoru a jeho strukturu byl studován metodami AAS, XRD, TPR, BET, N2O-RFC, TGA-MS, NH3-TPD a CO2-TPD

Does the structure of CuZn hydroxycarbonate precursors affect the intrinsic hydrogenolysis activity of CuZn catalysts?

A comparative study of the properties and hydrogenolysis activity of catalysts derived from single-phase CuZn precursors was carried out to elucidate the effect of the precursor structure on the catalyst activity in hydrogenolysis and to examine their potential to replace the classical CuCr catalysts. Three CuZn catalysts were prepared by co-precipitation aiming at Cu/Zn ratios of 0.7, 5.0 and 1.6 to obtain single-phase aurichalcite, zincian malachite and a mixture of both phases, respectively. The catalyst precursors were calcined at temperatures of 300 and 450 degrees C, reduced in situ and tested in dimethyl adipate hydrogenolysis. The properties of the precursors and catalysts were analyzed using in situ XRD, TGA-MS, TPR-H-2, nitrogen physisorption and N2O chemisorption methods. According to the characterization data, aurichalcite-derived catalysts had superior structural properties to zincian malachite-derived catalysts: smaller copper crystallites, larger total and copper surface areas, and stable surface areas during the experiment. Consequently, aurichalcite-derived catalysts outperformed catalysts prepared from zincian malachite in the studied range of phase and elemental CuZn compositions. Nonetheless, the calculated intrinsic hydrogenolysis activity of surface Cu sites (TOF) was similar for all three catalysts.Web of Science10103314330