Бурение грунтовых зондов, установка энергетических колодцев

The use of copper as the key element in CO and CO2 reduction cata­lysts is a well explored research area in heterogeneous catalysis.

The application of copper and copper/zinc catalysts for the syn­thesis of alcohols from syngas has been reviewed in three recent reviews [11,43,9]. Generally, copper and copper/zinc catalyst are well known [44] for reduction of CO to methanol, and during the preparation of these catalysts it has been noted that catalysts pre­cipitated with alkali normally give higher yield of higher alcohols during the methanol synthesis. The distribution of the higher alco­hol mixtures obtained on these catalysts depends on the promoter concentration, but methanol still remains the dominant product. These observations led to further explorations of addition of alkali metals to copper catalysts to produce higher alcohols [44].

A number of researchers have reported that alkali metals such as Cs or K on Cu-Zn-based catalysts Cu/ZnO, Cu/ZnO/Al2O3, and Cu/ZnO/Cr2O3, show maxima in selectivity toward ethanol and higher alcohols with increasing alkali loading [44]. This K or Cs promotion has been seen in Cu-Mg-based catalyst systems as well, where C2 oxygenate selectivity passed through a maximum with increasing K and Cs promoter content, and this may be due to the bifunctional nature of these alkali-promoted Cu-based catalysts. The bifunctional nature of the promoted catalyst can be explained as follows. As the Cu-Zn catalyst provides sites for hydrogenation, Cs or K and its counter ions provide basic sites that catalyze C-C and C-O bond-forming reactions. During the increasing of Cs or K promoter content, and when it reaches a critical proportion, alkali metals can block the Cu-Zn hydrogenation, thereby decreasing the ethanol production [45]. In the group I series of elements tested as alkali promoters, it has been found that selectivity toward higher alcohols followed the general trend Li < Na < K < Rb < Cs [46]. This may be due to the fact that basic promoters neutralize the acidity of catalysts and thus suppress the undesired reactions such as dehy­dration, isomerization, coke formation, and methanation [47]. For example, alkali metal Na or K, or a mixture of both, were necessary with Cu/Co/Cr2O3/ZnO catalysts to suppress methanol formation reaction at temperatures below 290°C [48].

Xu and Iglasia have studied the carbon-carbon bond forma­tion pathways during CO hydrogenation to higher alcohols using 13C-labeled carbon monoxide gas as the reactant and alkali-pro­moted Cu-based catalysts (K-CuMgCeOx and Cs-Cu/ZnO/Al2O3) [49]. They found that C-C bonds in ethanol are formed via two pathways, direct reactions of CO and direct coupling of CH3OH. On K-Cu0.5Mg5CeOx, direct reactions of CO are the predominant pathway for the initial C-C bond steps. On Cs-Cu/ZnO/Al2O3, eth­anol is predominantly formed via direct coupling of oxygen-con­taining C1 intermediates derived from CH3OH. Furthermore, they reported that Cs+ cations introduce a methanol-coupling pathway unavailable on catalysts without Cs promoter, leading to higher alcohol synthesis rates [49].

In another approach to understanding the C2 oxygenate for­mation on Cu catalysts, Goodarznia and Smith studied the methanol decomposition and C2-oxygenate formation on alkali — promoted Cu-MgO catalysts [50]. In this study the decomposi­tion of CH3OH in the presence of CO has been investigated over high surface area MgO, Cu-MgO, K-Cu-MgO and Cs-Cu-MgO catalysts. The catalysts were prepared by thermal decomposi­tion of metal salts mixed with palmitic acid. The reduced cata­lysts had surface areas of 18-74 m2 g-1 and intrinsic basicities of 4-17 pmol CO2 m-2. Results revealed that methyl formate was a primary product of CH3OH decomposition, whereas CO was a secondary product. They found that even though the selectivity to C2 species, ethanol, and acetic acid was low (< 5 C-atom %) at the low pressure (101 kPa), there was an optimum intrinsic basic­ity (9.5 pmol CO2 m-2) at which the selectivity to C2 species and methyl formate reached a maximum [50].

Another novel approach for ethanol production from syngas — derived dimethyl ether (DME), hydrogen and carbon monoxide has been proposed by Tsubaki’s group [51]. They have studied a sequential dual bed reactor with modified zeolite and Cu/ZnO cat­alysts, where a mixture of syngas and DME is used as the feed gas. Ethanol was directly synthesized from dimethyl ether (DME) and syngas (CO + H2) with the combination of Cu-modified H-Modenite (H-MOR) zeolite catalyst and metallic Cu/ZnO catalysts in a dual­catalyst bed reactor. An illustration of catalyst loading in the reactor is shown in Figure 13.4.

The methyl acetate (MA) was firstly formed by DME carbon — ylation on the upper zeolite catalyst layer, and then was subse­quently hydrogenated on the lower Cu/ZnO catalyst layer to be converted into ethanol accompanying with methanol. A copper — doped H-MOR catalyst prepared by ion-exchange method exhib­ited better catalytic activity compared with the pure H-MOR catalyst in the single DME carbonylation reaction, and the influ­ence of reaction temperature was investigated in detail, confirm­ing that the optimal reaction temperature for this copper doped

Methyl acetate

Figure 13.4 Illustration of catalyst loading in reactor: (a) the single zeolite catalyst for DME carbonylation, and (b) the dual-catalyst bed reactor for ethanol synthesis [51].

H-MOR catalyst was 493 K. For ethanol synthesis in dual-catalyst bed reactor, the combination of Cu/H-MOR catalyst with Cu/ZnO catalyst exhibited promoted performance, not only on catalytic activity, but also on the selectivity and productivity of ethanol, much better than that of the combination of pure H-MOR catalyst with Cu/ZnO catalyst [51].

A representative set of results from an experiment using a com­bination of H-MOR or Cu/H-MOR catalyst with Cu/ZnO catalyst for ethanol synthesis is shown in Table 13.7.

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