Method for deposition of noble metal nanoparticles on catalysts to promote same, and the compositions so produced

Abstract

A method for promoting the supported catalysts using noble metal nanoparticles. Different noble metal precursors are preferentially deposited onto the supported metal catalysts through Chemical vapor deposition (CVD), and compositions so produced. Further, the promoted catalyst is used for CO and CO.sub.2 hydrogenation reactions, increasing the reaction conversion, C.sub.5+ compounds selectivity and chain growth probability. The active phase of catalyst can be either cobalt oxide, nickel oxide or their reduced format (Co.sup.0 or Ni.sup.0), and the noble metal is preferably Ruthenium.

Claims

1. A method for producing a catalyst comprising: forming, on a support surface, an active metal surface of a precursor catalyst, wherein: the active metal surface of the precursor catalyst is selected from the group consisting of cobalt oxide, nickel oxide, reduced formats (Co.sup.0 or Ni.sup.0) and combinations thereof, and the support surface of the precursor catalyst is made of a material selected from the group consisting of -Al.sub.2O.sub.3, TiO.sub.2, carbon nanotubes or CNT, and combinations thereof; and depositing, via chemical vapor deposition, ruthenium metal nanoparticles onto the active metal surface, the depositing including reacting on the active metal surface of the precursor catalyst a ruthenium metal precursor vapor with a reactant gas, at a reacting temperature at which the precursor catalyst catalyzes a decomposition of the ruthenium metal precursor vapor into ruthenium metal nanoparticles, wherein the reacting temperature is below a temperature at which the ruthenium metal precursor vapor substantially deposits ruthenium metal nanoparticles upon the support surface of said precursor catalyst, and wherein the reacting temperature is within the range of about 150 C. to about 200 C.

2. The method according to claim 1, wherein the precursor catalyst is an alumina-supported cobalt catalyst.

3. The method according to claim 1, wherein said ruthenium is about 0.01% to 1% by weight of active metal.

4. The method according to claim 3, wherein said ruthenium is about 0.05% to 0.3% by weight of active metal.

5. The method according to claim 1, wherein the ruthenium metal nanoparticles are carried by Argon gas to said precursor catalyst.

6. The method according to claim 1, further comprising heating a sublimation zone of a chemical vapor deposition assembly to about 80 C.

7. The method according to claim 1, further comprising obtaining an Fourier Transform Infrared (FTIR) pattern of the ruthenium metal nanoparticles that have decomposed during the chemical vapor deposition.

8. A method for producing a catalyst comprising: depositing ruthenium metal nanoparticles onto first support surfaces using chemical vapor deposition of a ruthenium metal precursor to produce a first effluent; depositing ruthenium metal nanoparticles onto a first precursor catalyst using chemical vapor deposition of the ruthenium metal precursor to produce a second effluent, the first precursor catalyst including first active metal surfaces and second support surfaces; obtaining an Fourier Transform Infrared (FTIR) pattern of the first effluent and the second effluent for temperatures between 100 C. and 280 C.; and determining a preferential temperature range that extends between a first temperature and a second temperature, the first temperature corresponding to a temperature at which decomposition of the ruthenium metal precursor is detected in the second effluent, the second temperature corresponding to a temperature at which decomposition of the ruthenium metal precursor is detected in the first effluent, wherein the chemical vapor deposition of the ruthenium metal precursor in the preferential temperature range preferentially deposits ruthenium metal nanoparticles upon the first active metal surfaces and minimally deposits ruthenium metal nanoparticles upon the second support surfaces of the first precursor catalyst.

9. The method of claim 1, wherein the ruthenium metal precursor vapor includes ruthenocene vapor.

10. The method of claim 1, wherein the reactant gas includes hydrogen.

11. The method of claim 1, wherein the depositing further includes: concurrently carrying the ruthenium metal precursor vapor and the reactant gas onto the active metal surface of the precursor catalyst.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter that is regarded as forming the present invention, it is believed that the invention will be better understood from the following description taken in conjunction with the accompanying DRAWINGS, where like reference numerals designate like structural and other elements, in which:

(2) FIG. 1 is a representative illustration showing an exemplary hierarchical chart for an experimental procedure designed to find a preferred chemical vapor deposition (CVD) temperature window pursuant to the principles of the present invention;

(3) FIG. 2 illustrates exemplary thermogravimetry/differential thermal analysis (TG/DTA) and differential thermogravimetry (DTG) profiles of ruthenocene, such as in a nitrogen (N.sub.2) atmosphere with a heating rate of about 5 C./min in one embodiment of the present invention;

(4) FIG. 3 illustrates a Fourier Transform Infrared (FTIR) spectrum or spectroscopy of the decomposition products of ruthenocene pursuant to an embodiment of the instant invention;

(5) FIG. 4 is a schematic illustration of a chemical vapor deposition (CVD) experimental setup for practicing the principles of the present invention;

(6) FIG. 5 illustrates the areas of Fourier Transform Infrared (FTIR) absorbance for two scenarios in embodiments of the present invention, namely: (a) illustrating CC bond peak areas, and (b) illustrating CH bond peak areas, at various sublimation and decomposition temperatures for both -Al.sub.2O.sub.3 and Co/-Al.sub.2O.sub.3. A preferential CVD temperature window indicates the temperature range at which no ruthenocene decomposition occurs on the -Al.sub.2O.sub.3, while significant decomposition occurs on Co/-Al.sub.2O.sub.3;

(7) FIG. 6 illustrates respective Transmission Electron Microscopy (TEM), with nanoparticle size distribution inserts, and corresponding Energy Dispersive X-Ray (EDX) patterns for two scenarios, namely: (a) a CoRu0 unpromoted catalyst, and (b) a CoRu5 catalyst promoted with 0.3 wt % Ru, pursuant to the teachings of the instant invention;

(8) FIG. 7 illustrates lattice fringes of (a) a CoRu0 unpromoted catalyst and (b) a CoRu5 catalyst with 0.3 wt % Ru, as set forth hereinabove and described further hereinbelow in connection with FIG. 6 of the DRAWINGS, along with respective electron diffraction analyses (SAED) insets; and

(9) FIG. 8 illustrates various temperature programmed reaction (TPR) profiles for unpromoted and ruthenium promoted catalysts pursuant to embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(10) The following detailed description is presented to enable any person skilled in the art to make and use the invention. For purposes of explanation, specific nomenclature is set forth to provide a thorough understanding of the present invention. However, it will be apparent to one skilled in the art that these specific details are not required to practice the invention. Descriptions of specific applications are provided only as representative examples. Various modifications to the preferred embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the scope of the invention. The present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest possible scope consistent with the principles and features disclosed herein.

(11) As discussed, prior art and traditional methods for the preparation of promoted catalysts generally result in promoter impregnation on both the active phase of the catalyst and the support. However, Applicant has found that the highest promoting role of precious noble metals occur when the promoter is only impregnated on the active phase, with close contacts but not onto the surfaces of the support. The present invention cures the serious impediments found in the prior art and traditional techniques.

(12) As discussed, chemical vapor deposition (CVD) is preferably used for the addition of a promoter on the active phase surface of a catalyst with high bimetallic interaction, which, as noted, leads to higher catalytic performance than the prior art. Applicant has found that by fine tuning the temperature in a CVD temperature window, the noble metal precursor decomposes preferentially on the surface of the cobalt or nickel as the active phase of carbon oxides hydrogenation catalyst, with minimal amounts of noble metal deposition onto the surface of the support. Indeed, using the improved techniques of the present invention, the close contact between the catalyst active phase and the noble metal promoter greatly enhances the reducibility of the promoted catalysts and improves their activity and selectivity during hydrogenation reactions.

(13) In a first embodiment of the present invention, chemical vapor deposition of ruthenocene is applied for preferential deposition of ruthenium onto the cobalt of a Fischer-Tropsch synthesis catalyst. The close contact between cobalt and ruthenium greatly enhances the reducibility of the Ru-promoted cobalt catalysts and improves their Fourier Transform Spectroscopy (FTS) activity and selectivity.

(14) A preferred experimental procedure designed to find the CVD temperature window is illustrated in an exemplary hierarchical chart in FIG. 1 of the DRAWINGS, which sets forth eight preferably sequential steps for the procedure, i.e., numbered 1-8, as shown and pursuant to the teachings of the present invention. Either a support (e.g., -Al.sub.2O.sub.3, SiO.sub.2, TiO.sub.2, SBA-15, carbon nanotubes or CNT) or a catalyst sample (e.g., supported Co.sub.3O.sub.4 or NiO) was placed in the deposition zone of CVD reactor, as shown and described in more detail hereinbelow in connection with FIG. 4. Argon was passed through the sublimation zone in the CVD reactor, to carry the noble metal precursor vapor, without any decomposition, to the deposition zone of CVD reactor and reacted with reactant gas (e.g., H.sub.2, O.sub.2 or O.sub.3) on the surface of the sample. The CVD reactor effluents were then passed through a gas cell in an Fourier Transform Infrared (FTIR) or gas chromatography (GC) sample loop, as is understood in the art.

(15) As noted, the thermochemical decomposition byproducts of noble metal precursors, on the support and the catalyst at various temperatures are detected by FTIR or GC. The special sublimation and decomposition temperature ranges which the noble metal precursor decomposition rates on the surface of catalyst (supported Co.sub.3O.sub.4 or NiO) are much higher than the surface of support, promise an intimate contact between the catalyst active phase and deposited noble metal. This temperature range is termed the Preferential CVD Temperature Window, and is a central feature and object of the present invention. A detailed example, based on the aforesaid hierarch, is now presented for a CO hydrogenation (FTS) reaction.

(16) Co.sub.3O.sub.4/-Al.sub.2O.sub.3 Catalyst Preparation

(17) In this exemplary embodiment, an alumina-supported cobalt catalyst was prepared by impregnation of -Al.sub.2O.sub.3 with a cobalt nitrate aqueous solution. A sufficient amount of the cobalt nitrate was dissolved in de-ionized water to prepare about 15 wt % of cobalt onto the -Al.sub.2O.sub.3. The -Al.sub.2O.sub.3 was then immersed in a nitrate solution for about 1 hr, filtered, and dried in an evacuated oven at about 70 C. for about 4 hours, and then at about 120 C. overnight, afterwards calcined at about 400 C. for about 4 hours in air.

(18) CVD Precursor Selection

(19) In the present invention, ruthenocene was preferably used as precursor for the chemical vapor deposition of ruthenium. The ruthenocene vapor pressure equation is presented in equation (1):
log.sub.10(P[kPa])=135249.99/T[K](1)

(20) According to equation (1), the vapor pressures of ruthenocene are 0.013 and 0.084 kPa, respectively, at 80 and 100 C., which are the temperatures of a ruthenocene sublimation zone employed in this study.

(21) A thermal gravimetric analysis (TGA) of ruthenocene is illustrated in FIG. 2 of the DRAWINGS. As shown, the TGA curve exhibited a one-step weight loss to zero in the range of about 100-200 C., accompanying a sharp differential thermogravimetry (DTG) endothermic peak at about same temperature range. This indicates that ruthenocene completely sublimes at temperatures lower than about 200 C. in Argon, with no ruthenium residue as a ruthenocene decomposition product.

(22) CVD Reactant Gas Selection

(23) Hydrogen (H.sub.2) was utilized to accelerate the decomposition of ruthenocene in the decomposition zone of the CVD reactor. A sample FTIR spectrum of ruthenocene thermo-chemical destruction products in the region of about 400-4000 cm.sup.1 is depicted in FIG. 3 of the DRAWINGS.

(24) CVD setup for Ru deposition on Co.sub.3O.sub.4/-Al.sub.2O.sub.3

(25) With reference now to FIG. 4 of the DRAWINGS, there is illustrated an exemplary CVD experimental setup used for a presently-preferred technique for the deposition of ruthenium on Co.sub.3O.sub.4/-Al.sub.2O.sub.3 pursuant to the principles of the instant invention. As shown, the setup includes respective Argon (Ar) and a hydrogen (H.sub.2) feeding sections, a ruthenocene sublimation zone, a ruthenocene deposition zone, a condenser, and a gas cell in an FTIR for analysis of ruthenocene decomposition products in the effluent gases.

(26) As shown in FIG. 4, the feeding section has two mass flow controllers (MFC1 and MFC2) used to adjust the flow rates of Argon (Ar) and hydrogen (H.sub.2), respectively. A preferably Quartz CVD reactor includes the two lines for feeding the carrier gas (Ar) and the reactant gas (H.sub.2). Furthermore, the furnace preferably has two different temperature zones for the ruthenocene sublimation and decomposition, as shown by the arrows in FIG. 4. First, Ruthenocene is loaded into the sublimation zone of the CVD reactor, with Ar as the carrier gas. The Ruthenocene carried by the argon reaches the catalyst (Co.sub.3O.sub.4/Al.sub.2O.sub.3 samples, without prior reduction) loaded into the subsequent deposition zone in the CVD reactor, as shown, the temperature of which is high enough for the decomposition of the aforesaid ruthenocene with the aid of the H.sub.2 reactant gas. The reactor effluent gases were passed through the condenser to remove any unreacted organometallic compounds, and passed through a gas cell in an FTIR, which detects the decomposition products of ruthenocene, as described.

(27) Preferential CVD of Ruthenium on Cobalt of Co/-Al.sub.2O.sub.3

(28) As discussed, the present invention is directed to improved techniques to preferentially decompose ruthenocene on the surface of the cobalt, as the active phase of Co/-Al.sub.2O.sub.3 catalyst, with minimal or no amounts of ruthenium being deposited onto the surface of the alumina support. As discussed, this objective can be achieved by fine-tuning the temperature in a CVD temperature window. The following experimental procedure was designed to find the preferred CVD temperature windows pursuant to the teachings of the present invention.

(29) Either a -Al.sub.2O.sub.3 support or a Co.sub.3O.sub.4/-Al.sub.2O.sub.3 catalyst sample was placed in the deposition zone of CVD reactor, as shown and described in connection with FIG. 4. Argon was passed through the sublimation zone in CVD reactor, to carry the ruthenocene vapor, without any decomposition, to the deposition zone of CVD reactor, and reacted with hydrogen on the surface of the sample. The CVD reactor effluents were passed through the gas cell in the FTIR. The FTIR patterns for ruthenocene decomposition products on the -Al.sub.2O.sub.3 and the Co.sub.3O.sub.4/-Al.sub.2O.sub.3, at various temperatures, for both CC bonds and CH bonds, are detected.

(30) With reference now to FIG. 5 of the DRAWINGS, particularly the two graphs shown in the Figure, the areas under CC and CH show absorbances in the ranges of about 2900-3100 and about 1300-1500 cm.sup.1, respectively, which are plotted versus the decomposition zone temperature.

(31) Applicant has found that for all sublimation and decomposition temperatures, the ruthenocene decomposition rates on the Co.sub.3O.sub.4/-Al.sub.2O.sub.3 catalyst are significantly higher than those on -Al.sub.2O.sub.3., with the effect more pronounced at lower temperatures. In all cases, in the range of about 150-200 C., no ruthenocene decomposition occurs on the -Al.sub.2O.sub.3, while significant decomposition occurs on the Co.sub.3O.sub.4/-Al.sub.2O.sub.3. This temperature range, illustrated more particularly within the boxed sections within the two graphs, are labeled Preferential CVD Temperature Window. Cobalt oxide dispersed on the -Al.sub.2O.sub.3 seems to catalyze the ruthenocene decomposition. This promises an intimate contact between the cobalt active phase and deposited ruthenium.

(32) CVD Operating Conditions

(33) It should be understood that CVD experiments were performed at a sublimation temperature of about 80 C. and at a decomposition temperature of about 180 C. in about 15 sccm argon and about 50 sccm hydrogen, respectively. Also, 0.4 g calcined 15 wt % Co/-Al.sub.2O.sub.3 catalysts were promoted by Ru-contents of 0.05, 0.1, 0.15, 0.2 and 0.3 wt % Co by varying the preferential CVD times.

(34) As Applicant can be their own lexicographer, for convenience and clarity, the abbreviated name for 15 wt % Co.sub.3O.sub.4/-Al.sub.2O.sub.3 is CoRu0 and the promoted catalysts with 0.05 to 0.3 wt % of ruthenium are termed CoRu1 to CoRu5 (denoted CoRu5-180), respectively. Another CoRu5 sample was prepared by ruthenocene CVD at 225 C. (denoted as CoRu5-225), which is beyond the preferential CVD temperature window and ruthenocene decomposes on both alumina and cobalt oxide on alumina. FTIR spectrum shows the presence of ruthenocene decomposition products on alumina, as shown in FIG. 5.

(35) For comparison of a preferential CVD with the usual impregnation method, the CoRu5-SI, corresponding to a CoRu5 sample prepared by the CVD method, was prepared by impregnation of a RuCl3 solution onto the calcined Co.sub.3O.sub.4/-Al.sub.2O.sub.3. The sample was dried and then calcined at the same temperature of 400 C.

EXAMPLE 1

Properties of the Prepared CoRux Containing Catalysts

(36) With reference now to FIG. 6 of the DRAWINGS, there are shown Transmission Electron Microscopy (TEM) micrographs and Energy Dispersive X-Ray (EDX) analyses of CoRu5 containing about 0.3 wt % ruthenium and those of CoRuO. As shown, the EDX analysis of CoRu5 confirms the presence of ruthenium in the sample. The cobalt oxide nanoparticles size distributions of the samples are also shown in FIG. 6 insets within the respective TEM micrographs. As about 0.3 wt % Ru is added to the CoRuO, the average cobalt oxide nanoparticles sizes reduces from 14.4 to 8.9 nm and their distribution shifts to lower values and narrows down.

(37) Lattice fringes of CoRuO unpromoted catalyst and CoRu5 sample promoted with 0.3 wt % Ru are shown in FIG. 7 of the DRAWINGS. It should be understood that about 0.21 nm lattice fringes in CoRu5 samples can be attributed to Ru (1 0 1) crystallites, which are in intimate contact with cobalt oxide nanoparticles.

(38) An X-Ray diffraction (XRD) analysis, along with respective selected area electron diffraction analyses (SAEDs), was applied to investigate the effect of ruthenium on average Co.sub.3O.sub.4 crystallite sizes of the calcined Ru-Co/-Al.sub.2O.sub.3 catalysts. As shown, the crystallite size of Co.sub.3O.sub.4 decreases from about 15.8 to 8.9 nm, as the Ru content increases from about 0 to 0.3 wt % of cobalt, respectively. Table 1 hereinbelow indicates that the cobalt dispersion increases with the ruthenium content of catalysts. Also, as the ruthenium content of the catalysts increases to about 0.3 wt %, the surface area of the catalysts increases by about 37%. This may be due to a decrease in the cobalt oxide particle sizes, in accordance with the aforesaid XRD results.

(39) TABLE-US-00001 TABLE 1 Average Co.sub.3O.sub.4 crystallite size, Co crystallite size, dispersion and specific surface area of the catalysts samples. Nominal CVD Specific Co.sub.3O.sub.4 Co.sup.0 Hydrogen Ru content time Surface area Crystallite Crystal Dispersion.sup.c consumption in TPR Catalyst (wt % Co) (mn) (m.sup.2/gr) size.sup.a (nm) size.sup.b (nm) (%) (mol H.sub.2/g. catal.) -Al.sub.2O.sub.3 195 CoRu0 0.00 138 15.8 11.9 8.1 1772 CoRu1 0.05 5 178 14.2 10.7 9.0 2300 CoRu2 0.1 10 180 12.9 9.7 9.9 2474 CoRu3 0.15 15 183 11.8 8.9 10.8 2599 CoRu4 0.2 20 184 10.1 7.6 12.6 2757 CoRu5 0.3 30 189 8.9 6.7 14.3 3167 CoRu5-SI 0.3 182 12 9 10.6 2698 .sup.aCo.sub.3O.sub.4 crystallite size is determined using Scherrer's equation at 2 = 36.8 .sup.bCo and Co.sub.3O.sub.4 crytstallites size are related by d(Co) = 0.75d(Co.sub.3O.sub.4) .sup.c% D = 96/d(Co)

(40) With reference now to FIG. 8 of the DRAWINGS, there are illustrated various TPR profiles for Co/-Al.sub.2O.sub.3 catalyst and the ones promoted with ruthenium. As is known in the art, the presence of ruthenium in all of the catalysts shifts the two main reduction peaks to lower temperatures. Thus, the more ruthenium is deposited on the Co/-Al.sub.2O.sub.3, the more the TPR peaks shift to lower temperatures. The ruthenium structural promotion requires intimate contact between cobalt and ruthenium components. The promotion of supported cobalt catalysts with ruthenium, using the traditional, prior art impregnation method, apparently leads to the migration of ruthenium onto the catalyst active phase, as well as the support. As shown in the present invention, the promotional effect can be enhanced if the ruthenium has a close contact with the cobalt active phase. The preferred CVD method and techniques set forth in the present invention provides conditions for preferential deposition of ruthenium on the surface of the cobalt active phase rather than -alumina support. This intimate contact between ruthenium and cobalt significantly decreases the first and second peak temperatures in TPR profile. As compared to CoRuO, the first and second TPR peaks of CoRu5-180, as prepared by the preferred CVD herein, are shifted by 134 and 120 C. to lower temperatures, while that of CoRu5-SI, prepared by the traditional impregnation method are shifted by much lower values of 80 and 50 C., respectively, due to a better structural promotion of ruthenium in CoRu5 sample. In addition, as compared to CoRu5-180, the cobalt oxides reduction peaks of CoRu5-225 have shifted to higher temperatures as those of CoRu5-SI. This indicates that a significant amount of Ru is deposited on the alumina without intimate contact with cobalt oxide.

EXAMPLE 2

The use of Promoted Catalyst for CO Conversion

(41) CO conversion, product selectivity and chain growth probability (a), as well as olefin to paraffin ratio in C.sub.2-C.sub.4 hydrocarbons, for the Fischer-Tropsch synthesis (FTS) on the various catalysts at 220 C. and H.sub.2/CO=2, and mean space time of 4 s are summarized in Table 2 hereinbelow.

(42) As shown, as the ruthenium content increases from 0 in CoRu0 to 0.3 wt % Ru in CoRu5, several things occur: (a) the CO conversion increases by 2.8 times, (b) the selectivity to methane (as one of the most undesirable products) decreases by about 28%, (c) in accordance to a, the selectivity to C.sub.5+ as the most desirable FTS products increases by 46.4%, (d) the O/P ratio decreases by 2.4 times, and (e) the selectivity to C.sub.2-C.sub.4 does not change significantly.

(43) It is also observed that, in addition to the beneficial aspects noted hereinabove, C.sub.5+ selectivity increases by adding ruthenium by the preferential CVD method. As compared to CoRu5-180, the corresponding CoRu5-SI prepared by the traditional impregnation method has higher CH.sub.4 and lower C.sub.5+ selectivities and about 45% lower CO conversion. Also, significantly lower CO conversion and C.sub.5+ selectivity are observed for CoRu5-225.

(44) Therefore, the CoRu5-180 catalyst has 270% higher C.sub.5+ yields than the CoRuO unpromoted cobalt catalyst which is much higher than C.sub.5+ yields of CoRu5-SI prepared by the traditional impregnation method that has 82% higher C.sub.5+ yields with respect to CoRuO sample.

(45) TABLE-US-00002 TABLE 2 Catalytic performances of Co/-Al.sub.2O.sub.3 with different Ru content. CO Conver- sion Selectivity (O/P) Carbon Catalysts (%) C.sub.1 C.sub.2-C.sub.4 C.sub.5+ % Balance CoRu0 15.3 37 29 34 0.64 8.1 99.9 CoRu1 24.7 29.9 28 42.1 0.70 5.1 99.6 CoRu2 26.8 27.9 28.2 43.9 0.73 4.7 99.2 CoRu3 31.1 26.9 26.7 46.4 0.73 4.6 99.4 CoRu4 40.1 26.8 28.9 44.3 0.73 3.4 99.5 CoRu5-180 42.9 26.6 28.5 44.9 0.74 3.4 99.9 CoRu5-225 28.8 27.1 30.6 42.3 0.72 4.4 99.1 CoRu5-SI 23.7 28 32 40 0.68 5.1 99.3 *Reaction Conditions: T = 220 C., P = 1 bar, H.sub.2/CO = 2, = 4 s

(46) While the present invention has been illustrated by the description of the embodiments thereof, and while the embodiments have been described in detail, it is not the intention of the Applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative apparatus and method, and illustrative examples shown and described. Accordingly, departures may be made from such details without departure from the breadth or scope of the applicant's concept. Furthermore, although the present invention has been described in connection with a number of exemplary embodiments and implementations, the present invention is not so limited but rather covers various modifications and equivalent arrangements, which fall within the purview of the appended claims.