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Highlights: [•] Adsorption structure of 1,4-butanediol on Er2O3 was elucidated by DFT calculation. [•] Interaction of 1,4-butanediol with Er2O3 was calculated by PIO theory. [•] Tridentate adsorption of 1,4-butanediol on Er2O3 accelerated the dehydration into 3-buten-1-ol. [•] Reaction mechanism in the dehydration of 1,4-butanediol over Er2O3 was elucidated. [•] The reaction proceeds via acid–base concerted mechanism over Er2O3. [Copyright &y& Elsevier]

The aim of this work is to develop an effective catalyst for the conversion of butanediols, which is derivable from biomass, to valuable chemicals such as unsaturated alcohols. The dehydration of 1,4-, 1,3-, and 2,3-butanediol to form unsaturated alcohols such as 3-buten-1-ol, 2-buten-1-ol, and 3-buten-2-ol was studied in a vapor-phase flow reactor over sixteen rare earth zirconate catalysts at 325 °C. Rare earth zirconates with high crystallinity and high specific surface area were prepared in a hydrothermal treatment of co-precipitated hydroxide. Zirconates with heavy rare earth metals, especially Y2Zr2O7 with an oxygen-defected fluorite structure, showed high catalytic performance of selective dehydration of 1,4-butanediol to 3-buten-1-ol and also of 1,3-butanediol to form 3-buten-2-ol and 2-buten-1-ol, while the zirconate catalysts were less active in the dehydration of 2,3-butanediol. The calcination of Y2Zr2O7 significantly affected the catalytic activity of the dehydration of 1,4-butanediol: a calcination temperature of Y2Zr2O7 at 900 °C or higher was efficient for selective formation of unsaturated alcohols. Y2Zr2O7 with high crystallinity exhibits the highest productivity of 3-buten-1-ol from 1,4-butanediol at 325 °C. [ABSTRACT FROM AUTHOR]

Vapor-phase catalytic dehydration of 2,3-butanediol (2,3-BDO) was investigated over rare earth oxide catalysts and In 2 O 3 at around 400 °C. In the dehydration of 2,3-BDO over Sc 2 O 3 , 1,3-butadiene was mainly produced together with butanone, 2-methyl-propanal, 2-methyl-propanol, 3-buten-2-ol, and butene isomers. Sc 2 O 3 calcined at 800 °C showed the highest 1,3-butadiene yield of 88.3% at 411 °C in H 2 carrier gas flow. Since 3-buten-2-ol is produced selectively from 2,3-BDO over Sc 2 O 3 at a low temperature of 325 °C, 3-buten-2-ol rather than butanone is a probable intermediate from 2,3-BDO to 1,3-butadiene. 3-Buten-2-ol is readily converted into 1,3-butadiene at temperatures lower than 411 °C over Sc 2 O 3 and Al 2 O 3 . In addition, double-bed catalysts composed of an upper catalyst bed of Sc 2 O 3 and a lower of Al 2 O 3 successfully converted 2,3-BDO directly into 1,3-butadiene with a stable selectivity higher than 94% at 318 °C and 100% conversion of 2,3-BDO. [ABSTRACT FROM AUTHOR]

Highlights: [•] Dehydration of 3-methyl-1,3-butanediol into 3-methyl-3-buten-1-ol was investigated. [•] Carbon-modified alumina showed high selectivity to 3-methyl-3-buten-1-ol at 200°C. [•] The C-modified alumina was prepared by depositing coke using 3-methyl-3-buten-1-ol. [•] The selectivity to 3-methyl-3-buten-1-ol was increased by the coke content over Al2O3. [•] Formation of by-products such as isobutylene decreased by the coke deposition. [ABSTRACT FROM AUTHOR]

Abstract: Dehydration of butanediols into unsaturated alcohols was investigated over CeO2 with different particle sizes. The size was controlled by the calcination temperature. Catalytic performance in the dehydration of 1,3-butanediol is greatly affected by the particle size. The selectivity to unsaturated alcohols such as 3-buten-2-ol and trans-2-buten-1-ol increases with increasing the particle size, while decomposition of 1,3-butanediol into methanol and ethanol is catalyzed by CeO2 with small particles. In contrast, in the reaction of 1,4-butanediol, cyclization products such as tetrahydrofuran and γ-butyrolactone increases with decreasing the particle size, instead of the decomposition into methanol and ethanol. CeO2{111} facets became predominant on the large particles, whereas different surfaces such as {100} and {110} facets were exposed on the small CeO2 particles. In the dehydration of butanediols, CeO2 has structure-sensitive catalysis: CeO2{111} facets have active sites for the formation of unsaturated alcohols, and the other surfaces catalyze the side reactions such as decomposition of 1,3-butanediol and cyclization of 1,4-butanediol. [Copyright &y& Elsevier]

Vapor-phase dehydration of 1,4-butanediol and 3-buten-1-ol to produce 1,3-butadiene was investigated over rare earth oxides such as Lu 2 O 3 , Yb 2 O 3 , Tm 2 O 3 , Er 2 O 3 , and Sc 1.0 Yb 1.0 O 3 . In the dehydration of 3-buten-1-ol, heavy rare earth oxides such as Lu 2 O 3 , Yb 2 O 3 , and Er 2 O 3 showed high catalytic performance for the selective formation of 1,3-butadiene with producing small amount of propylene whereas acidic catalysts such as alumina decomposed 3-buten-1-ol into propylene. In particular, over Yb 2 O 3 calcined at 800 °C, 3-buten-1-ol was converted with a yield of 1,3-butadiene higher than 95% at 340 °C. In the dehydration of 1,4-butanediol, furthermore, we developed an efficient catalytic system: 1,3-butadiene was produced via an intermediate, 3-buten-1-ol, over Yb 2 O 3 with an excellent yield of 96% at 360 °C and a high contact time of 2.26 h. Yb 2 O 3 successfully inhibited the major side reaction such as decomposition of 3-buten-1-ol to propylene and provided the selective production of 1,3-butadiene from 1,4-butanediol. [ABSTRACT FROM AUTHOR]

Review: 134 refs. [ABSTRACT FROM AUTHOR]

Vapor-phase catalytic dehydration of 1,4-butanediol (1,4-BDO) was investigated over modified ZrO 2 catalysts. In the dehydration of 1,4-BDO over monoclinic ZrO 2 (m-ZrO 2 ), an unsaturated alcohol, 3-buten-1-ol (3B1OL), was produced together with tetrahydrofuranand γ-butyrolactone. Among alkaline earth metal oxide modifiers, CaO with an appropriate content significantly enhanced the 3B1OL selectivity of m-ZrO 2 . The modification of CaO was more efficient over m-ZrO 2 than tetragonal ZrO 2 . CO 2 -TPD measurements reveal that CaO supported on m-ZrO 2 calcined at 800 °C or higher generated new basic sites, which are attributed from Ca-O-Zr hetero-linkages, for the effective formation of 3B1OL from 1,4-BDO. In order to create more Ca-O-Zr hetero-linkages on the m-ZrO 2 surface efficiently, additional ZrO 2 was loaded on m-ZrO 2 together with CaO via a co-impregnation method. At an appropriate weight ratio of CaO/ZrO 2 = 7/2 loaded on m-ZrO 2 , both the 1,4-BDO conversion and the 3B1OL selectivity were enhanced greatly. Especially, the 3B1OL selectivity exceeded 90% at 350 °C. [ABSTRACT FROM AUTHOR]

Vapor-phase catalytic dehydration of 2,3-butanediol (2,3-BDO) to produce 3-buten-2-ol (3B2OL) was investigated over several monoclinic ZrO 2 (m-ZrO 2 ) catalysts modified with alkaline earth metal oxides (MOs), such as SrO, BaO, and MgO, to compare with the previously reported CaO/m-ZrO 2 . It was found that these modifiers enhanced the 3B2OL formation to the same level as CaO did by loading an appropriate MO content. Among all the tested catalysts, the BaO/m-ZrO 2 calcined at 800 °C with a low BaO content (molar ratio of BaO/ZrO 2 = 0.0452) shows the highest 2,3-BDO conversion (72.4%) and 3B2OL selectivity (74.4%) in the initial stage of 5 h at 350 °C. In order to characterize those catalysts, their catalytic activities, crystal structures, and basic properties were studied in detail. In X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) experiment, it was elucidated that highly dispersed M-O-Zr (M = Ca, Sr, and Ba) hetero-linkages were formed on the surface by loading these MOs onto m-ZrO 2 with an appropriate content and then calcining at 800 °C. It can be concluded that the M-O-Zr hetero-linkages generate the proper base-acid balance for the efficient formation of 3B2OL from 2,3-BDO. [ABSTRACT FROM AUTHOR]

• Vapor-phase catalytic dehydration of 3-methyl-1,3-butanediol was investigated over Y 2 Zr 2 O 7 catalysts. • During the hydrothermal (HT) aging, residual nitrates in the precursor slurry were removed, and the slurry was crystallized. • In the HT aging at 200 °C, the precursor slurry was crystalized into Y 2 Zr 2 O 7 for 2 h or longer. • The HT aging time significantly influenced the acid-base properties of the Y 2 Zr 2 O 7 , which affected the catalytic activity. • The isoprene yield over Y 2 Zr 2 O 7 catalyst calcined at 900°C was 82.4% at 375 °C and a time on stream of 10 h. Vapor-phase dehydration of 3-methyl-1,3-butanediol to produce isoprene was investigated over Y 2 Zr 2 O 7 catalysts prepared by hydrothermal aging at 200 °C with various aging times. Removal of residual species such as nitrate and crystallization of Y 2 Zr 2 O 7 proceeded during the hydrothermal aging. The X-ray diffraction analysis confirmed the progression of the Y 2 Zr 2 O 7 crystal growth during hydrothermal aging from 0 to 24 h, with no significant change afterward. The hydrothermal aging time of up to 4 h significantly influenced the acid-base properties of the Y 2 Zr 2 O 7 catalysts, which consecutively affected their catalytic performance. At a reaction temperature of 375 °C, the conversion of 3-methyl-1,3-butanediol and the selectivity to isoprene over Y 2 Zr 2 O 7 catalyst calcined at 900 °C were 100 and 82.4% at a time on stream of 10 h, respectively. Reaction mechanisms were also proposed in consideration for the results of dehydration of intermediate unsaturated alcohols. [Display omitted] [ABSTRACT FROM AUTHOR]

Vapor-phase catalytic dehydration of 2,3-butanediol was investigated over metal oxides such as CeO2, La2O3, Yb2O3, ZrO2, Al2O3, TiO2, ZnO, Fe2O3, NiO, and Cr2O3. In the dehydration of 2,3-butanediol, 3-buten-2-ol was preferentially produced over monoclinic ZrO2 along with major by-products such as butanone and 3-hydroxy-2-butanone. Over ZrO2 calcined at 900°C, 3-buten-2-ol was produced with a maximum selectivity of 59.0% at 300°C without producing 1,3-butadiene. [ABSTRACT FROM AUTHOR]

Vapor-phase catalytic dehydration of 2,3-butanediol (2,3-BDO) to form 1,3-butadiene (BD) via 3-buten-2-ol (3B2OL) was studied over various single metal oxide catalysts. Among the catalysts, Sc 2 O 3 prepared under hydrothermal (HT) conditions at 200 °C followed by 800 °C calcination showed the most excellent catalytic activity. The crystallization of precursor ScOOH during HT aging noticeably enhances the catalytic activity of the resulting Sc 2 O 3 for the formation of 3B2OL in the dehydration of 2,3-BDO. The formation rate of 3B2OL from 2,3-BDO over the HT-aged Sc 2 O 3 was twice as high as Sc 2 O 3 without HT aging. Calcination temperatures of Sc 2 O 3 are also important: calcination at 800 °C is efficient for the selective formation of 3B2OL from 2,3-BDO. The HT-aged Sc 2 O 3 also showed an excellent catalytic activity for the formation of BD with the yield higher than 80% in the dehydration of 2,3-BDO at 411 °C. [Display omitted] [ABSTRACT FROM AUTHOR]

• Vapor-phase catalytic dehydration of 1,4-butanediol was investigated over Y 2 Zr 2 O 7 catalysts. • 1,3-Butadiene together with 3-buten-1-ol, tetrahydrofuran, and propylene was produced depending on the conditions. • 1,3-Butadiene yield of 90% or higher was achieved over the Y 2 Zr 2 O 7 calcined at 700 °C in the dehydration at 360 °C. • An unsaturated alcohol such as 3-buten-1-ol is more reactive than 1- and 2-butanol over the Y 2 Zr 2 O 7 catalyst. • It is suggested that the C=C double bond of 3-buten-1ol affects an attractive interaction to anchor the Y 2 Zr 2 O 7 catalyst. Vapor-phase catalytic dehydration of 1,4-butanediol (1,4-BDO) was investigated over Y 2 O 3 -ZrO 2 catalysts. In the dehydration, 1,3-butadiene (BD) together with 3-buten-1-ol (3B1OL), tetrahydrofuran, and propylene was produced depending on the reaction conditions. In the dehydration over Y 2 O 3 -ZrO 2 catalysts with different Y contents at 325°C, Y 2 Zr 2 O 7 with an equimolar ratio of Y/Zr showed high selectivity to 3B1OL, an intermediate to BD. In the dehydration at 360°C, a BD yield higher than 90% was achieved over the Y 2 Zr 2 O 7 calcined at 700°C throughout 10 h. In the dehydration of 3B1OL over Y 2 Zr 2 O 7 , however, the catalytic activity affected by the calcination temperature is roughly proportional to the specific surface area of the sample. The highest activity of Y 2 Zr 2 O 7 calcined at 700 °C for the BD formation from 1,4-BDO is explained by the trade-off relation in the activities for the first-step dehydration of 1,4-BDO to 3B1OL and for the second-step dehydration of 3B1OL to BD. The higher reactivity of 3B1OL than saturated alcohols such as 1-butanol and 2-butanol suggests that the C=C double bond of 3B1OL induces an attractive interaction to anchor the catalyst surface and promotes the dehydration. A probable mechanism for the one-step dehydration of 1,4-BDO to BD was discussed. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • CaO-stabilized ZrO 2 (CSZ) with high surface area was prepared via hydrothermal aging at 200 °C. • The hydrothermal aging of precursor hydroxide promotes crystallization of CSZ in NH 3 aqueous media. • Aging in NaOH/KOH aq. induced growth of crystallites to reduce the specific surface area of CSZ. • CSZ aged in NH 3 aq. followed by calcination at 900 °C was active in the dehydration of 1,4-butanediol. • The resulted CSZ exhibited the highest 3-buten-1-ol selectivity of 89.2 % at 325 °C. Calcia-stabilized zirconia (CSZ) samples were prepared under hydrothermal (HT) conditions for an efficient catalyst in the vapor-phase dehydration of 1,4-butanediol (1,4-BDO). Preparative aspects of CSZ for the efficient catalyst were discussed. Ammonia aqueous media in the HT aging were effective for high crystallinity of tetragonal/cubic CSZ with high specific surface area, which resulted in high catalytic performance in the dehydration of 1,4-BDO while not all Ca in the solution was included in ZrO 2 precipitates in the ammonia media. Although almost all Ca was included in ZrO 2 in the strong basic KOH/NaOH aqueous solution, the CSZ samples aged in the strong basic media, which were composed of mainly CaZrO 3 crystallite, were readily sintered resulting in poor catalytic activity. Sr cations as well as Ca cations were included in ZrO 2 to stabilize cubic ZrO 2 , while small amounts of Mg and Ba cations were included in ZrO 2 not to stabilize the cubic ZrO 2 structure. Among the alkaline earth cations, Ca was the most effective in enhancement of catalytic activity in the dehydration of 1,4-BDO. CSZ with a Ca content of 9.4 mol% calcined at 900 °C exhibited the highest 3-buten-1-ol selectivity of 89.2 % at a 1,4-BDO conversion of 54.7 % at 325 °C. [ABSTRACT FROM AUTHOR]

[Display omitted] • Vapor-phase dehydration of 1,3-butanediol was investigated over oxygen-defected Yb 2 Zr 2 O 7 catalysts. • An efficient oxygen-defected Yb 2 Zr 2 O 7 catalyst was prepared through a hydrothermal treatment at 200 °C. • Catalytic activity was significantly affected by calcination temperature of Yb 2 Zr 2 O 7 catalysts. • Unsaturated alcohols such as 3-buten-2-ol and 2-buten-1-ol were preferentially produced in the dehydration. • Stable conversion of 1,3-butanediol with high unsaturated alcohols selectivity of 96.0% was obtained at 325 °C. Vapor-phase dehydration of 1,3-butanediol was performed over Yb 2 O 3 -ZrO 2 catalysts in an ambient nitrogen atmosphere. Catalysts were prepared by a hydrothermal (HT) method as well as a coprecipitation method. The Yb 2 O 3 -ZrO 2 sample prepared by HT was confirmed to be crystallites of oxygen-defected type cubic Yb 2 Zr 2 O 7 , while the as-prepared coprecipitation sample was amorphous. The HT samples had high specific surface areas as ca. 40 m2 g−1 even after calcined at temperatures higher than 800 °C, whereas the coprecipitation samples without HT was readily sintered at the high temperatures. The best catalytic performance was obtained over HT Yb 2 O 3 -ZrO 2 catalyst calcined at 900 °C: the total selectivity to unsaturated alcohols was higher than 95% at a 1,3-butanediol conversion of 82% at 325 °C. The structure of active sites and the reaction mechanism of the dehydration of 1,3-butanediol were discussed. We proposed that an oxygen defect site on the stable (111) face of cubic Yb 2 Zr 2 O 7 would provide an active site, and that Zr4+, Yb3+, and O2- exposed on the defect could coordinate with a 1,3-butanediol molecule to form a tridentate coordination structure, which possibly initiate the dehydration to produce unsaturated alcohols through a base-acid concerted mechanism. [ABSTRACT FROM AUTHOR]